Multidimensional arrays in JavaScript and several ways to sort them. Arrays in JavaScript JS Data output from multidimensional array
- I. BRAIN OF PRESENT MACHINES
- Foreach method and related methods
- Cycle for
- Proper use of the Cycle for ... In
- Cycle for ... of (implicit use of iterator)
- Explicit use of iterator
- Using methods for extinguishing real arrays
- Transformation into a real array
- Note on Objects
I. BRAIN OF PRESENT MACHINES
At the moment there are three ways of busting elements of the real array:- aRRAY.PROTOTYPE.FOREACH method;
- classic Cycle for;
- "Right" built Cycle for ... in.
- cycle for ... of (implicit use of iterator);
- explicit use of the iterator.
1. Foreach method and related methods
If your project is designed to support ECMAScript 5 (ES5) standards, you can use one of its innovations - Foreach method.Example of use:
var a \u003d ["a", "b", "c"]; a.Foreach (Console.log (Entry);));
In general, the use of Foreach requires an ES5-SHIM emulation library for browsers that do not have native support for this method. These include IE 8 and earlier versions that are still used in some places.
The advantages of Foreach belongs that it does not need to declare local variables to store the index and the value of the current element of the array, as they are automatically transmitted to the callback function (columns) as arguments.
If you are concerned about the possible cost of calling the columus for each element, do not worry and read it.
Foreach is designed to enjoy all the elements of the array, but besides it, ES5 offers several more useful methods for the bust of all or certain elements plus performances with any actions with them:
- every - Returns True if for each element of the columus array returns the value given to True.
- some - Returns True, if at least for one element of the columus array returns the value given to True.
- filter - creates a new array, including those elements of the source array for which the columns return TRUE.
- map - creates a new array consisting of values \u200b\u200bof obscene columns.
- reduce - reduces an array to a single value by applying colums in turns to each element of the array, starting from the first (it can be useful for calculating the amount of array elements and other outcome functions).
- reduceright - works similarly to reduce, but moves the items in the reverse order.
2. Cycle for
Good old for steering:Var a \u003d ["a", "b", "c"]; Var Index; For (index \u003d 0; index< a.length; ++index) {
console.log(a);
}
If the length of the array is unchanged during the entire cycle, and the cycle itself belongs to the productivity of the code (which is unlikely), then you can use a "more optimal" version for with the storage of the array length:
Var a \u003d ["a", "b", "c"]; Var Index, Len; for (index \u003d 0, len \u003d a.length; index< len; ++index) {
console.log(a);
}
Theoretically, this code must be performed slightly faster than the previous one.
If the procedure for the bore of the elements is not important, then you can go even further in terms of optimization and get rid of the variable to store the length of the array by changing the procedure for the reverse:
Var a \u003d ["a", "b", "c"]; Var Index; for (index \u003d a.length - 1; index\u003e \u003d 0; --index) (console.log (a);)
However, in modern JavaScript engines such games with optimization usually do not mean anything.
3. Proper use of the Cycle for ... In
If you advise you to use the for ... in cycle, remember that the enumeration of arrays is not what it is for what it is intended. Contrary to common misconception cycle for ... IN It is not the array indexes, but the listed properties of the object.Nevertheless, in some cases, such as busting sparse arrays, for ... in may be useful if only precautions are followed as shown in the example below:
// A - Raised Array Var A \u003d; a \u003d "a"; a \u003d "b"; a \u003d "c"; For (VAR KEY IN A) (IF (A.HaSownProperty (KEY) && / \u003d$$|^ MD*$/.Test(Key) && Key<= 4294967294) {
console.log(a);
}
}
In this example, two checks are performed on each iteration of the cycle:
- the fact that the array has its own property with the name Key (not inherited from its prototype).
- the fact that Key is a string containing a decimal record of an integer whose value is less than 4294967294. Where does the last number come from? From the definition of an array index in the ES5, from which it follows that the greatest index that can have an element in the array: (2 ^ 32 - 2) \u003d 4294967294.
In order not to write such a bulky check code every time the massif is required, it is possible to arrange it as a separate function:
Function ArrayhasownIndex (Array, Key) (Return Array.hasownProperty (Key) && / \u003d Type$|^ MD*$/.Test(Key) && Key<= 4294967294;
}
Then the body of the cycle from the example will significantly reduce:
For (IF (ARRAYSOWNINDEX (A, KEY)) (Console.log (A);))
The audit code discussed above is universal suitable for all cases. But instead you can use a shorter version, although formally and not quite correct, but, nevertheless, suitable for most cases:
For (i.hasownProperty (Key) && String (Parseint (Key, 10)) \u003d\u003d\u003d Key) (Console.log (a);))
4. Cycle for ... of (implicit use of iterator)
ES6, while still being in the status of draft, should enter iterators in JavaScript.Iterator
- This is a protocol implemented by an object that determines the standard method for obtaining a sequence of values \u200b\u200b(finite or infinite).
The iterator is an object in which the Next () method is defined - a function without arguments that return an object with two properties:
- done (Boolean) - takes True if the iterator reached the end of the resultant sequence. Otherwise, has a false value.
- value - determines the value returned by the iterator. It may not be defined (absent) if the Done property is true.
An example of using for ... of:
VAR VAL; var a \u003d ["a", "b", "c"]; FOR (VAL OF A) (Console.log (VAL);)
In the above example, the for ... of an implicitly calls an array object iterator to obtain each array value.
5. Explicit use of iterator
Iterators can also be used and explicitly, however, in this case the code becomes much more complicated, compared with the For ... of the cycle. It looks like this:Var a \u003d ["a", "b", "c"]; var it \u003d a.entries (); Var Entry; While (! (entry \u003d it.next ()). Done) (Console.log (entry.value);)
In this example, the array.prototype.Entries method returns an iterator that is used to display the values \u200b\u200bof the array. Each iteration entry.value contains an array of the form [key, value].
II. Bust of massive-like objects
In addition to real arrays, JavaScript is also found massive-like objects . With real arrays, their relatives are related to the fact that they have the property of Length and properties with names in the form of numbers corresponding to the elements of the array. You can call the Nodelist DOM collection and pseudomassive arguments available inside any function / method.1. Using ways of extinguishing real arrays
At least most, if not all, methods of extinguishing real arrays can be applied to enumerate massive-like objects.The designs for and for ... in can be applied to massively like objects exactly the same way as to real arrays.
Foreach and other ARRAY.PROTOTYPE methods are also applicable to massive objects. To do this, use the file.call or function.apply call.
For example, if you want to apply Foreach to the property of the Childnodes object Node, then this is done like this:
Array.prototype.foreach.call (Node.Childnodes, Function (Child) (// Make anything with the object Child));
For ease of reuse of this reception, you can declare a link to the array.prototype.Foreach method in a separate variable and use it as a reduction:
// (It is assumed that all the code below is in one area of \u200b\u200bvisibility) var foreach \u003d array.prototype.Foreach; // ... foreach.call (Node.Childnodes, Function (Child) (// Make something with the Child object));
If an array-like object is an iterator, it can be used explicitly or implicitly for the integrity of the object in the same way as for real arrays.
2. Conversion to this array
There is also another, very simple, a way to enumerate an arms-like object: convert it into a real array and use any of the methods of existing arrays discussed above. For conversion, you can use the universal array.prototype.slice method, which can be applied to any massive object. It is done very simply as shown in the example below:Var truearray \u003d array.protype.slice.call (ArrayLikeObject, 0);
For example, if you want to convert the Nodelist collection to a real array, you need approximately such a code:
Var divs \u003d array.prototype.slice.call (Document.QuerySelectorall ("DIV"), 0);
Update.: As noted in Rock and Torbasow comments, in ES6 instead of array.prototype.slice, you can use a more visual array.From method.
3. Note on objects of execution environment
If you apply ARRAY.PROTOTYPE methods to the objects of the execution environment (such as DOM collection), then you should keep in mind that the correct operation of these methods is not guaranteed in all execution environments (including in browsers). It depends on the behavior of a particular object in a specific exercise environment, if more precisely, from how an abstract Hasproperty operation is implemented in this object. The problem is that the ES5 standard itself allows the possibility of incorrect behavior of the object with respect to this operation (see §8.6.2).Therefore, it is important to test the work of array.prototype methods in each execution environment (browser), in which you plan to use your application.
Greetings to all who are interested in such a topic as JavaScript multidimensional arrays and sorting. In the current publication, I will try in all details to disclose this topic.
Therefore, after reading the article, you will learn why multidimensional arrays are used in web applications, how they are created and how they can be controlled and sorted. Let's start learning!
How are multidimensional arrays are created and what are they needed for?
To begin with, it is necessary to remember how the usual one-dimensional array is created.
var Array \u003d.
And now remember that the multidimensional array is an array array.I agree, sounds like Tavtology. However, read the definition again. Indeed, the multidimensional array consists of a certain number of nested in it.
Consider the following situation. At the beginning of a kind of game, the user enters its name, and after graduating from it, the rating table with the names of the players and their records is displayed.
It is clear that such information is stored in the database. But when we pull it out of the database, we get a multidimensional array. After all, in each reducing the player login and the number of points scored.
It will look like this will be as follows:
var Results \u003d [["Markus", 333], ["Natasha", 211], ["Alexey", 124]];
As you can see, the information can be stored heterogeneous. It can be lines, and numbers, and even. This is possible because arrays are ineptized.
In this case, the appeal to the elements occurs through a double operator.
To secure the material, analyze a small program.
Value results \u003d
Arrays are a fairly convenient tool for storing ordered integrated data when processing them. In addition, working with them is very convenient and at the same time the speed of their processing is quite high.
Ways to sorting data
For arrays in JavaScript-e there is a built-in method called sort (). This tool is very flexible. And now I will explain why.
If you are using the method without parameters, it automatically streams the submarines on the first element in alphabetical order. So when calling rESULTS.sort () The disassembled object will look like this:
Alexey, 124.
Marcus, 333.
Natasha, 211.
And if you change the elements in each embedded array in each embedded array, it will turn out:
124, Aleksey
211, Natasha
333, Marcus
In this case, for comparison, all items are temporarily converted to lines.
If, to solve some particular task, you need a function sorting elements by a non-standard way, you can write it yourself and transferred to the parameter in sort (). It should be noted that the user function must return:
- a positive number (mainly selected 1) if the first specified element follows the second when compared;
- negative number (usually -1) if the second selected item must follow first;
- zero if two values \u200b\u200bare valued.
As an example, let's initial array rESULTS. Sort the points. What the results will be ordered from greater than less. This can be implemented in two ways.
In the first version, I changed the sorting logic, i.e. In a situation where you need to return a positive number, I return the negative and vice versa.
Record Table:
But in the second way, left the logic of sorting untouched, but used an additional one method - rEVERSE (). As can be seen from the name, Reverse changes the order of the elements to the opposite.
Therefore, the SORT () function will look like this:
| 1 2 3 4 5 | FUNCTION RECORDSORT (A, B) (IF (A\u003e B) RETURN 1; ELSE If (A< b) return -1; else return 0; } |
fUNCTION RECORDSORT (A, B) (IF (A\u003e B) RETURN 1; ELSE If (A< b) return -1; else return 0; }
But after it add the method specified above.
The output is made in the same way.
I want to draw your attention to one important point. When using these functions, all changes occur with the array to which you apply them. Thus, if you need to save the initial data type, then create a copy, and then edit it already.
Well, here I told about multidimensional arrays and their sorting. If you like the article, then subscribe to the blog and read other no less interesting publications. I would be grateful for the reposit. To new meetings!
Bye Bye!
Sincerely, Roman Chuechev
In the previous article we talked about what and how to work with it. In this article we will talk about multidimensional array.
This is an array that has one or more elements, is also arrays. Depending on the depth of the announcement, in particular it may be called two-dimensional array(2 levels) or three-dimensional array(3 levels) or four-dimensional(4 levels) and so on.
The most popular, after a one-dimensional array, which is most often used by this two-dimensional array. It is his, we will study in more detail.
As you can see, the elements of the two-dimensional array are one-dimensional arrays. If these one-dimensional arrays contained more arrays, then the array of Arr would have been three-dimensional.
For example, let's create three simple arrays and fill them with data. We are filled with even numbers, second fill in odd numbers, and the third by some arbitrary data.
// We declare three empty varies VAR Evennumbers \u003d New Array (); // variable k - for indexes of an array of Evennumbers var k \u003d 0; var oddnumbers \u003d new array (); // Variable N - for the indexes of the ODDNUMBERS VAR N \u003d 0 array; var data \u003d new array ("Car", "Plane", True, 89, "M"); // Fill the Evennumbers array, with even numbers for (var i \u003d 1; I
In order to see what is located inside the array can be used by such a tool as console..
For example, we want to see the contents of an array with odd numbers oddnumbers. To do this, in the code below we write to such a string:
Console.log (oddnumbers);
To see the result, you need to open console in browser. In Google Chrome it is done like this: Press the right click of the mouse on the page, and select the "View code" option from the context menu, that is, the inspector. In the English version, this option is called InSpect.
And the developer toolbar will appear below. It needs to go to the Console tab.
Now in order to create a two-dimensional array, It is necessary to declare it, and add one-dimensional arrays to it, which created above.
// declare a two-dimensional array of twoodimens, and fill it with VAR TWODIMENS \u003d New Array (Evennumbers, Oddnumbers, DATA); Console.log (TwoDimens);
Let's look at the console content of this array.
bust a two-dimensional array
To begin with, learn how to turn to the elements of a two-dimensional array.
As with single arrays, the appeal to the elements is made according to their indices.
For example, let's remove to the screen, an element with an index 3 of an array with odd numbers (oddnumbers). The one-dimensional ODDNUMBER array index in the TwoDimens two-dimensional array is equal to one (1).
Document.Write ("An index with an index 3 of an array of odd numbers Oddnumbers is:" + TwoDimens); // Element: 7
In the twodimens array, we appeal to an index element 1. The element that is under this index is an Oddnumbers array. And in this array, we already appeal to an element with an index 3, which is a number 7.
Now let's start the issue how to move a two-dimensional array.
The bust of the two-dimensional array is made using a double cycle. For example, we will make a bust of our array twodimens.
For (var i \u003d 0; i< twoDimens.length; i++){ for(var j = 0; j < twoDimens[i].length; j++){ document.write("
Element with index "+ i +" "+ j +" equal to: "+ twodimens [i] [j] +"
"); } }In the first cycle, we make a brute force of the TWodimens massif. In the second cycle, we already have a bust of the element itself (array). At first, the variable i is 0. Therefore, in the second cycle, we first make the first Evennumbers array, which has an index 0. And already inside the second cycle we appeal to the elements of this array. Thus: twodimens [j]. Where J varies from 0 to the length of the Evennumbers array.
After the generation of elements from the first array, we return to the first cycle, we increment the variable i, and go to the mischief of the second Oddnumbers array, which has an index 1. And so the bust of each element of the two-dimensional TWodimens array is made.
Now let's look at the result of this search:
That's all what I wanted to tell in this article. Now you know how to create a two-dimensional array, as you turn to the elements of the two-dimensional array and how to overdone a two-dimensional array. I hope that everything was clear. I wish you great success!
Arrays
Array - This is an ordered collection of values. Values \u200b\u200bin array are called elements, and each element is characterized by a numerical position in an array called an index. JavaScript arrays are inepesed: the array elements may have any type, and different elements of the same array can have different types. The elements of the array may even be objects or other arrays, which allows you to create complex data structures, such as arrays of objects and array of arrays.
The countdown of arrays in the JavaScript language begins with scratch and 32-bit integers are used for them - the first element of the array has an index 0. Arrays in JavaScript are dynamic: they may increase and decrease in size as needed; There is no need to declare the fixed sizes of arrays when creating or re-distribute memory when the size changes.
JavaScript arrays are a specialized form of objects, and array indices mean a little more than just the names of the properties that coincide are integers.
Massive creation
It is easiest to create an array with the help of a literal that is a simple list of split elements of an array in square brackets. The values \u200b\u200bin the literal of the array do not have to be constants - it can be any expressions, including literals of objects:
Var empty \u003d; // Empty array VAR Numbers \u003d; // Array with five numeric elements VAR MISC \u003d [1.1, TRUE, "A",]; // 3 of the element of different types + final comma Var Base \u003d 1024; var table \u003d; // array with variables var arrobj \u003d [,]; // 2 array inside containing objects
The syntax of literal arrays allows you to insert an optional final comma, i.e. The literal [,] corresponds to the array with two elements, and not with three.
Another way to create an array is to call a constructor Array (). Call the constructor in three different ways:
Call a designer without arguments:
Var arr \u003d new array ();
In this case, an empty array will be created, an equivalent literary.
Call a constructor with a single numeric argument that determines the length of the array:
Var Arr \u003d New Array (10);
In this case, an empty array of said length will be created. This form of the constructor call array () can be used to pre-distribute memory for an array if the amount of its elements is known in advance. Please note that at the same time no values \u200b\u200bare saved in the array.
It is clearly indicated in the constructor call the values \u200b\u200bof the first two or more elements of an array or one unlicas element:
Var arr \u003d new array (5, 4, 3, 2, 1, "test");
In this case, the constructor arguments become the values \u200b\u200bof the elements of the new array. The use of literal arrays is almost always easier than similar use of the Array () designer.
Reading and writing an array elements
Access to the elements of the array is carried out using the operator. To the left of the brackets should be the link to the array. Inside the brackets should be an arbitrary expression that returns non-negative meaning. This syntax is suitable for reading and recording the value of the array element. Consequently, all the following JavaScript instructions are allowed:
// Create an array with one element VAR ARR \u003d ["WORLD"]; // Read the element 0 var value \u003d arr; // Record the value in the element 1 Arr \u003d 3.14; // Record the value in the element 2 i \u003d 2; Arr [i] \u003d 3; // Record the value in the element 3 arr \u003d "hello"; // Read the elements 0 and 2, record the value in the element 3 ARR] \u003d ARR;
Let me remind you that arrays are a specialized variety of objects. Square brackets used to access the array elements act in the same way as square brackets used to access the properties of the object. The JavaScript interpreter converts numeric indexes specified in the brackets into the string - index 1 turns into a string "1" - and then uses strings as properties names.
There is nothing special in the conversion of numeric indexes in the line: the same can be done with conventional objects:
Var OBJ \u003d (); // Create a simple object OBJ \u003d "One"; // index it with integers
The feature of the arrays is that when using names of properties that are non-negative integers, arrays automatically determine the property value length.. For example, an array array with a single element was created above. Then the values \u200b\u200bof its elements with indexes 1, 2 and 3. As a result of these operations, the value of the Length properties of the array changed and became equal to 4.
It is necessary to clearly distinguish indexes in the array from the names of the properties of objects. All indexes are properties names, but only properties with names presented by integers are indexes. All arrays are objects, and you can add properties to them with any names. However, if you affect the properties that are array indexes, arrays respond to it, updating the value of the Length property if necessary.
Please note that negative and not numbers are allowed as array indices. In this case, the numbers are converted into strings that are used as properties.
Adding and removing array elements
We have already seen that the easiest way to add items to the array is to assign values \u200b\u200bto new indexes. To add one or more elements to the end of the array, you can also use the method push ():
Var arr \u003d; // Create an empty array arr.push ("zero"); // Add value to the end arr.push ("One", 2); // add two more values
Add an element to the end of the array can also, assigning the value to the ARR element. To insert an item to the beginning of the array, you can use the method unshift ()At the same time, the existing elements in the array are shifted in position with higher indices.
You can delete an array elements using the Delete statement as the usual properties of objects:
Var arr \u003d; Delete Arr; 2 in arr; // False, index 2 in the array is not defined by Arr.Length; // 3: The Delete operator does not change the LengTh property of the array
The removal of the element resembles (but is somewhat different) assigning the value undefined to this element. Please note that the application of the Delete statement to the array element does not change the value of the Length property and does not shift down the elements with higher indexes to fill the emptiness left after removing the item.
In addition, it is possible to remove elements in the end of the array by simply assigning the new value to the Length property. Arrays have a method pOP () (The opposite method Push ()), which reduces the length of the array by 1 and returns the value of the remote element. There is also a method shift () (The opposite method unshift ()), which removes the element at the beginning of the array. Unlike the Delete statement, the SHIFT () method shifts all the elements down to the position below their current indexes.
Finally there is a multi-purpose method sPLICE ()allowing you to insert, delete and replace the elements of arrays. It changes the value of the Length property and shifts an array elements with lower or high indices as needed. We will analyze all these methods a little later.
Multidimensional arrays
JavaScript does not support "real" multidimensional arrays, but it makes it easy to imitate them using arrays from arrays. To access the data item in an array of arrays, it is enough to use the operator twice.
For example, suppose that the MATRIX variable is an array of arrays of numbers. Each MATRIX [X] element is an array of numbers. To access a specific number in an array, you can use the expression MATRIX [X] [Y]. The following is a specific example, where the two-dimensional array is used as a multiplication table:
// Create a multidimensional array VAR Table \u003d New Array (10); // Table 10 strings FOR (var i \u003d 0; I
ARRAY class methods
ECMAScript 3 standard defines a lot of convenient features for working with arrays, which are available as methods of any array, as part of Array.Prototype. These methods will be presented in the following subsections.
Join ()
The array.join () method converts all the elements of the array in the string, combines them and returns the resulting string. In an optional argument, the method can be transferred to the string that will be used to separate items in the result string. If the separator string is not specified, the comma is used. For example, the following fragment gives a string "1,2,3":
Var arr \u003d; arr.join (); // "1,2,3" arr.join ("-"); // "1-2-3"
Reverse ()
The array.reverse () method changes the order of the elements in the array to the opposite and returns a reordered array. The permutation is performed directly in the source array, i.e. This method does not create a new array with reordered elements, and reorders them in an existing array. For example, the following fragment where Reverse () and JOIN () methods are used, results in a string "3,2,1":
Var arr \u003d; arr.reverse (). join (); // "3,2,1"
Sort () method
The array.sort () method sorts the elements in the source array and returns a sorted array. If the SORT () method is called without arguments, sorting is performed in alphabetical order (for comparison, items are temporarily converted into strings if necessary). Uncertain elements are transferred to the end of the array.
For sorting in any other order other than the alphabetic, Sort () method, you can transfer the comparison function as an argument. This feature sets which of its two arguments should follow before in the sorted list. If the first argument must precede the second, the comparison function must return a negative number. If the first argument should follow the second in the sorted array, the function must return the number greater than zero. And if two values \u200b\u200bare equivalent (i.e., the order of them is not important), the comparison function must return 0:
Var arr \u003d; arr.sort (); // Alphabetical order: 1111, 222, 33, 4 ARR.SORT (FUNCTION (A, B) (// Numeric order: 4, 33, 222, 1111 RETURN AB; // Returns a value of 0 // depending on the order of sorting a and b)); // we sort in the opposite direction, from more to less ARR.SORT (RETURN B-A));
Please note how convenient it is used in this fragment unnamed function. The comparison function is used only here, so there is no need to give her a name.
Concat () method
The array.concat () method creates and returns a new array containing the elements of the source array for which the Concat () method was called, and the values \u200b\u200bof all arguments transmitted by the Concat () method. If any of these arguments itself is an array, its elements are added to the returned array. However, it should be noted that the recursive transformation of the array of arrays into a one-dimensional array does not occur. The concat () method does not change the source array. Below are several examples:
Var arr \u003d; arr.concat (4, 5); // return arr.concat (); // Return Arr.Concat (,) // return arr.concat (4,]) // return]
Slice ()
The array.slice () method returns a fragment, or a submassion specified by the array. Two method arguments define the beginning and end of the returned fragment. The returned array contains an element whose number is indicated in the first argument, plus all subsequent elements, up to (but not including) the element whose number is specified in the second argument.
If only one argument is specified, the returned array contains all elements from the initial position to the end of the array. If any of the arguments has a negative value, it defines the number of the element relative to the end of the array. So, the argument -1 corresponds to the last element of the array, and the argument -3 is the third element of the array from the end. Here are some examples:
Var arr \u003d; arr.slice (0.3); // return Arr.Slice (3); // return Arr.Slice (1, -1); // return arr.slice (-3, -2); // Robn
SPLICE ()
The array.splice () method is a universal method performing an insert or removal of an array elements. Unlike Slice () and Concat () methods, the SPLICE () method changes the source array relative to which it was called. Please note that Splice () and Slice () methods have very similar names, but perform completely different operations.
The SPLICE () method can delete elements from the array, insert new items or perform both operations at the same time. The elements of the array, if necessary, are displaced, continuous sequence after inserting or removal.
The first argument of the SPLICE () method determines the position in the array, starting with which the insert and / or removal will be performed. The second argument determines the number of elements that must be removed (cut) from the array. If the second argument is omitted, all the elements of the array are removed from the array specified to the end. The SPLICE () method returns an array of remote elements or (if none of the items have been removed) an empty array.
The first two arguments of the SPLICE () method () determine the elements of the array to be removed. For these arguments, any number of additional arguments that determine the elements that will be inserted into an array starting from the position indicated in the first argument.
Var arr \u003d; arr.splice (4); // return, arr \u003d arr.splice (1,2); // return, arr \u003d arr.splice (1,1); // returns; arr \u003d arr \u003d; arr.splice (2.0, "a", "b"); // returns; Arr \u003d.
Push () and POP () methods
Push () and pop () methods allow working with arrays as with stacks. The Push () method adds one or more new elements to the end of the array and returns it a new length. The POP () method performs a reverse operation - removes the last element of the array, reduces the length of the array and returns the value remand. Note that both of these methods change the source array, and do not create a modified copy.
UNSHIFT () and SHIFT () methods
UNSHIFT () and SHIFT () methods behave almost the same as Push () and POP (), except that they insert and remove the elements at the beginning of the array, and not at the end. The unshift () method displays the existing elements towards large indices to release the location, adds an element or elements to the beginning of the array and returns a new array length. The SHIFT () method deletes and returns the first element of the array, shifting all the subsequent elements to one position down to occupy the location released at the beginning of the array.
Good day. In touch, Alexey Gulein. In the last article, we disassemble the SWITCH Case design in JavaScript. In this article, I would like to tell what arrays in JavaScript. The concept of the array plays an important role not only in JavaScript, but also in all programming. A variable, such as an array, contains in itself not one element, but several. The syntax of creating an array is as follows:
Var mas \u003d new array (value1, value2, ..., value);
In this case, a variable MAS is created by an array with the values \u200b\u200bspecified in brackets. I draw your attention to that the array is created using the new keyword. You can access the elements of the array by specifying the name of the array and in square brackets the array index. The array index is set from zero. Let's give an example of an array consisting of 4 elements and withdraw 2 element:
If we deliver the MAS, then the "privet" will be displayed, since the indexing of the array begins with scratch. Let's now understand how to output all the elements of the array. To do this, use the cycle. In addition to the knowledge of cycles in JavaScript, it is necessary to know the property of the Length arrays, which returns the number of array elements (or in its other length). Let's bring the length of the MAS massif:
The withdrawal of all elements of the array:
So far, we looked at one-dimensional arrays. In general, arrays can be multidimensional. The main thing must be understood that, for example, a two-dimensional array is an array of the elements of which are arrays. Let's analyze such a task with you: you need to create a two-dimensional array 3 to 3, the elements of which are specified by the user and output this array. Here we will use the PROMPT statement to request the number of user:
In our case, the two-dimensional array corresponds to (for example) such a structure: MAS \u003d [,,,]. It can be seen that the array of 3 elements, each of which is an array itself.
Initially, the JavaScript task was to make dynamic sites. In my practice, I have not used two-dimensional arrays anywhere, only one-dimensional, so that those knowledge on the arrays that you received from this article will be quite enough. In one of the following articles, I will tell about the array object, its properties and methods.