Array.prototype.unshift()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
unshift() 方法會添加一個或多個元素至陣列的開頭，並且回傳陣列的新長度。
嘗試一下
const array1 = [1, 2, 3];
console.log(array1.unshift(4, 5));
// Expected output: 5
console.log(array1);
// Expected output: Array [4, 5, 1, 2, 3]
語法
arr.unshift(element1[, ...[, elementN]])
參數
elementN-
欲添加至陣列開頭的元素。
回傳值
呼叫此方法之物件的新 length 屬性值。
描述
範例
js
var arr = [1, 2];
arr.unshift(0); // 執行後的結果是3，其代表處理後的陣列長度
// 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]
規範
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-array.prototype.unshift |