Array.prototype.unshift()

unshift() 方法 (method) 增加一個或多個元素 (element) 到陣列的開頭，並回傳新陣列的長度。

var a = [1, 2, 3];
a.unshift(4, 5);

console.log(a); // [4, 5, 1, 2, 3]

語法

arr.unshift([element1[, ...[, elementN]]])

參數

elementN

加到陣列最前端的元素。

回傳值

The new length property of the object upon which the method was called.

描述

unshift 方法把給予的值插入到與陣列相似的物件開頭。

unshift 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

var arr = [1, 2];

arr.unshift(0); // result of call is 3, the new array length
// arr is [0, 1, 2]

arr.unshift(-2, -1); // = 5
// arr is [-2, -1, 0, 1, 2]

arr.unshift([-3]);
// arr is [[-3], -2, -1, 0, 1, 2]

規格

瀏覽器相容性

相關資料

• Array.prototype.push()
• Array.prototype.pop()
• Array.prototype.shift()