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JavaScript method unshift() adds one or more elements to the beginning of an array and returns the new length

黄舟Original: 2017-11-04 09:37:3215739browse

Definition and Usage

The unshift() method adds one or more elements to the beginning of the array and returns the new length.

Syntax

arrayObject.unshift(newelement1,newelement2,....,newelementX)

Parameters	Description
newelement1	Required. The first element added to the array.
newelement2	Optional. The second element added to the array.
newelementX	Optional. Several elements can be added.

Return value

The new length of arrayObject.

Description

The unshift() method will insert its parameters into the head of arrayObject and move existing elements to higher subscripts sequentially to leave space . The first argument to the method will become the new element 0 of the array, if there is a second argument it will become the new element 1, and so on.

Please note that the unshift() method does not create a new creation, but directly modifies the original array.

Tips and Comments

Comments: This method will change the length of the array.

Note: The unshift() method does not work correctly in Internet Explorer!

Tip: To add one or more elements to the end of the array, use the push() method.

Example

In this example, we will create an array, add an element to the beginning of the array, and return the new length of the array:

<script type="text/javascript">

var arr = new Array()
arr[0] = "George"
arr[1] = "John"
arr[2] = "Thomas"

document.write(arr + "<br />")
document.write(arr.unshift("William") + "<br />")
document.write(arr)

</script>

Output:

George,John,Thomas
4
William,George,John,Thomas

Example:

<html>
<head>
<title>JavaScript Array unshift Method</title>
</head>
<body>
<script type="text/javascript">
var arr = new Array("orange", "mango", "banana", "sugar");
 
var length = arr.unshift("water");
document.write("Returned array is : " + arr );
document.write("<br /> Length of the array is : " + length );
 
</script>
</body>
</html>

This will produce the following results:

Returned array is : water,orange,mango,banana,sugar
Length of the array is : 5

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JavaScript method unshift() adds one or more elements to the beginning of an array and returns the new length

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