Clear, define, and delete javascript Array Operations

Js arrays have various operations. Next I will introduce how to clear, define, and delete js arrays, and also introduce array sorting. You are welcome to refer to them.

Let's take a look at how to clear the js array.

When an array needs to be cleared, many people use the following method:

A = [];

We know that javascript variable storage methods can be divided into reference types and direct quantities. The array belongs to the object, that is, the reference type. It references the variable pointer address, which is designed to save memory.

In addition, if the preceding empty array method is used to assign a new array directly, the previously referenced array may not be released (with other references ), for example, the following code:

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Var a = [2, 3]; Var B =; A = []; Console. log (B );

At this time, a and B are not the same array. After a is cleared, B still refers to the referenced address. unless you mean it, this will pose a risk.

Therefore, the best way to empty the array is to set the length to 0, that is:

 

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A. length = 0;

Create and access js Arrays

Array Creation
 

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Var arrayObj = new Array (); // create an Array Var arrayObj = new Array ([size]); // create an Array and specify the length. Note that the length is not the upper limit. Var arrayObj = new Array ([element0 [, element1 [,... [, elementN]); // create an Array and assign values

 
 
It should be noted that, although the second method creates an array with a specified length, the array actually gets longer in all cases, that is, even if the length is 5, you can still store elements outside the specified length. Note: The length will change accordingly.

2. Access to array elements

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Var testGetArrValue = arrayObj [1]; // obtain the element value of the array. ArrayObj [1] = "this is a new value"; // assign a new value to the array element

 
 

3. Add array elements

 

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Code ArrayObj. push ([item1 [item2 [... [itemN]); // Add one or more new elements to the end of the array and return the new length of the array. ArrayObj. unshift ([item1 [item2 [... [itemN]); // adds one or more new elements to the array. The elements in the array are automatically removed and the new length of the array is returned. ArrayObj. splice (insertPos, 0, [item1 [, item2 [,... [, itemN]); // insert one or more new elements to the specified position of the array. The inserted element is automatically removed and "" is returned "".

Js array Conversion

1. convert an array to a string (concatenate an array element into a string using a character)

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Var a, B; A = new Array (0, 1, 2, 3, 4 ); B = a. join ("-");

 

2. convert a string to an array (cut the string into several strings based on a specific character and return the string as an array)

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Var s = "abc, abcd, aaa "; Ss = s. split (","); // separate each comma.

Delete array elements

Var arr = ['A', 'B', 'C'];

To delete 'B', you can use either of the following methods:

1. delete method: delete arr [1]

In this way, the length of the array remains unchanged. In this case, the arr [1] is changed to undefined, but the index of the original array remains unchanged. In this case, you need to traverse the array element before using it.

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For (index in arr) { Document. write ('Arr ['+ index +'] = '+ arr [index]); }

　

This Traversal method skips the undefined element.

// It is often used to reconstruct the array through traversal.
　

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Array. prototype. remove = function (dx) { If (isNaN (dx) | dx> this. length) {return false ;} For (var I = 0, n = 0; I <this. length; I ++) { If (this [I]! = This [dx]) { This [n ++] = this [I] } } This. length-= 1 } A = ['1', '2', '3', '4', '5']; Alert ("elements:" + a + "nLength:" + a. length ); A. remove (0); // Delete the element whose subscript is 0 Alert ("elements:" + a + "nLength:" + a. length );

Array common functions

ToString (): converts an array into a string.
ToLocaleString (): converts an array into a string.
Join (): converts an array into a string connected with symbols.
Shift (): removes an element from the array header.
Unshift (): insert an element in the header of the array.
Pop (): deletes an element from the end of the array.
Push (): Add an element to the end of the array.
Concat (): add elements to the array
Slice (): returns the part of the array
Reverse (): sorts arrays in reverse order.
Sort (): sorts arrays.
Splice (): insert, delete, or replace an array element.