Array.prototype.shift()

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shift() 方法 (method) 會從陣列移除第一個元素 (element),並回傳該元素。此方法會改變陣列的長度。

var a = [1, 2, 3];
a.shift();

console.log(a); // [2, 3]

語法

arr.shift()

回傳值

移除的元素。

描述

The shift method removes the element at the zeroeth index and shifts the values at consecutive indexes down, then returns the removed value. If the length property is 0, undefined is returned.

shift is intentionally generic; this method can be called or applied to objects resembling arrays. Objects which do not contain a length property reflecting the last in a series of consecutive, zero-based numerical properties may not behave in any meaningful manner.

範例

從陣列移除單個元素

以下的程式碼會印出 myFish 陣列移除第一個元素之前跟之後的內容,也印出了移除的元素:

var myFish = ['angel', 'clown', 'mandarin', 'surgeon'];

console.log('myFish before: ' + myFish);
// "myFish before: angel,clown,mandarin,surgeon"

var shifted = myFish.shift(); 

console.log('myFish after: ' + myFish); 
// "myFish after: clown,mandarin,surgeon" 

console.log('Removed this element: ' + shifted); 
// "Removed this element: angel"

規格

Specification Status Comment
ECMAScript 3rd Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262)
The definition of 'Array.prototype.shift' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Array.prototype.shift' in that specification.
Standard  
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Array.prototype.shift' in that specification.
Draft  

瀏覽器相容性

Feature Chrome Firefox (Gecko) Edge Internet Explorer Opera Safari
Basic support 1.0 1.0 (1.7 or earlier) (Yes) 5.5 (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

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