Summary of methods for adding and deleting elements to JavaScript array Array objects_javascript skills

The examples in this article summarize the methods of adding and deleting elements to JavaScript array Array objects. Share it with everyone for your reference. The specific analysis is as follows:

pop method

Removes the last element in the array and returns that element.
arrayObj.pop( )
The required arrayObj reference is an Array object.
Description
If the array is empty, undefined will be returned.

shift method

Removes the first element in the array and returns that element.
arrayObj.shift( )
The required arrayObj reference is an Array object.
Description
The shift method removes the first element from an array and returns that element.

Copy code The code is as follows:

var arr = new Array(0,1,2,3,4);
var remove = arr.pop();
alert(remove);
alert(arr.length);

Remove and return the last element, pop 4 first, then prompt the current array length and pop 4!

push method

Adds a new element to an array and returns the array's new length value.
arrayObj.push([item1 [item2 [. . . [itemN ]]]])
Parameters
arrayObj
Required. An Array object.
item, item2,. . . itemN
Optional. The new element of this Array.
Description
The push method will add new elements in the order they appear. If one of the arguments is an array, the array is added to the array as a single element. If you want to combine elements from two or more arrays, use the concat method.

Copy code The code is as follows:

var arr = new Array(0,1,2,3,4);
// The parameter is one or more
var len = arr.push(5,6);
//len = arr.push(7);
for(var i=0;i alert(arr[i]);
}

You can add multiple ones at once, or you can add one and return the current length of the array. Print the contents of the array to observe the changes!

splice method

Removes one or more elements from an array, inserts a new element at the position of the removed element if necessary, and returns the removed element.
arrayObj.splice(start, deleteCount, [item1[, item2[, . . . [,itemN]]]])
Parameters
arrayObj
Required. An Array object.
start
Required. Specifies the starting position to remove elements from the array, starting from 0.
deleteCount
Required. The number of elements to remove.
item1, item2,. . .,itemN
Required. A new element to be inserted at the location of the removed element.
Description
The splice method modifies arrayObj by removing a specified number of elements starting from the start position and inserting new elements. The return value is a new Array object consisting of the removed elements.

Copy code The code is as follows:

var arr = new Array(0,1,2,3,4);
// Delete the two elements starting from 2, starting from 0
// Return the array with removed elements
var reArr = arr.splice(2,2);
// You can replace the new element with the removed element
//Just add new elements from the removal starting position. If you remove two elements, you can add 10 new elements
//var reArr = arr.splice(2,2,6,7,8,9);
for(var i=0;i alert(arr[i]);
}

If you don't want to add new elements, just don't pass the third parameter!

concat method (Array)

Returns a new array that is a combination of two or more arrays.
array1.concat([item1[, item2[, . . . [, itemN]]]])
Parameters
array1
Required. The Array object to which all other arrays are to be concatenated.
item1,. . ., itemN
Optional. The other item to be connected to the end of array1.
Description
The concat method returns an Array object containing the concatenation of array1 and any other items provided.
The items to be added (item1...itemN) will be added to the array in order from left to right. If an item is an array, add its contents to the end of array1. If the item is not an array, it is added to the end of the array as a single array element.

The following is copying elements from the source array to the result array:

Object parameters copied from an array being concatenated to a new array still point to the same object after copying. No matter which one of the new array and the source array is changed, it will cause the other to change.
Only the value of a numeric or string concatenated into a new array is copied. Changing the values ​​in one array does not affect the values ​​in the other array.

Copy code The code is as follows:

var arr = new Array(0,1);
var arr2 = new Array(3,4);
var arr = arr.concat(arr2);
for(var i=0;i alert(arr[i]);
}

The function of the method is to copy the elements in arr2 to arr!

I hope this article will be helpful to everyone’s JavaScript programming design.