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• 句法
• 描述
• Polyfill
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

copyWithin() method shallow copies part of an array to another location in the same array and returns it without modifying its length.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

句法

arr.copyWithin(target[, start[, end]])
					

参数

target

Zero-based index at which to copy the sequence to. If negative, target will be counted from the end.

若 target is at or greater than arr.length , nothing will be copied. If target is positioned after start , the copied sequence will be trimmed to fit arr.length .

start 可选

Zero-based index at which to start copying elements from. If negative, start will be counted from the end.

若 start 被省略， copyWithin will copy from index 0 .

end 可选

Zero-based index at which to end copying elements from. copyWithin copies up to but not including end . If negative, end will be counted from the end.

若 end 被省略， copyWithin will copy until the last index (default to arr.length ).

返回值

The modified array.

描述

copyWithin works like C and C++'s memmove , and is a high-performance method to shift the data of an Array . This especially applies to the TypedArray method of the same name. The sequence is copied and pasted as one operation; pasted sequence will have the copied values even when the copy and paste region overlap.

copyWithin function is intentionally generic , it does not require that its this value be an Array 对象。

copyWithin method is a mutable method. It does not alter the length of this , but it will change its content and create new properties, if necessary.

Polyfill

if (!Array.prototype.copyWithin) {
  Object.defineProperty(Array.prototype, 'copyWithin', {
    value: function(target, start/*, end*/) {
    // Steps 1-2.
    if (this == null) {
      throw new TypeError('this is null or not defined');
    }
    var O = Object(this);
    // Steps 3-5.
    var len = O.length >>> 0;
    // Steps 6-8.
    var relativeTarget = target >> 0;
    var to = relativeTarget < 0 ?
      Math.max(len + relativeTarget, 0) :
      Math.min(relativeTarget, len);
    // Steps 9-11.
    var relativeStart = start >> 0;
    var from = relativeStart < 0 ?
      Math.max(len + relativeStart, 0) :
      Math.min(relativeStart, len);
    // Steps 12-14.
    var end = arguments[2];
    var relativeEnd = end === undefined ? len : end >> 0;
    var final = relativeEnd < 0 ?
      Math.max(len + relativeEnd, 0) :
      Math.min(relativeEnd, len);
    // Step 15.
    var count = Math.min(final - from, len - to);
    // Steps 16-17.
    var direction = 1;
    if (from < to && to < (from + count)) {
      direction = -1;
      from += count - 1;
      to += count - 1;
    }
    // Step 18.
    while (count > 0) {
      if (from in O) {
        O[to] = O[from];
      } else {
        delete O[to];
      }
      from += direction;
      to += direction;
      count--;
    }
    // Step 19.
    return O;
  },
  configurable: true,
  writable: true
  });
}
					

范例

Using copyWithin

[1, 2, 3, 4, 5].copyWithin(-2)
// [1, 2, 3, 1, 2]
[1, 2, 3, 4, 5].copyWithin(0, 3)
// [4, 5, 3, 4, 5]
[1, 2, 3, 4, 5].copyWithin(0, 3, 4)
// [4, 2, 3, 4, 5]
[1, 2, 3, 4, 5].copyWithin(-2, -3, -1)
// [1, 2, 3, 3, 4]
[].copyWithin.call({length: 5, 3: 1}, 0, 3)
// {0: 1, 3: 1, length: 5}
// ES2015 Typed Arrays are subclasses of Array
var i32a = new Int32Array([1, 2, 3, 4, 5])
i32a.copyWithin(0, 2)
// Int32Array [3, 4, 5, 4, 5]
// On platforms that are not yet ES2015 compliant:
[].copyWithin.call(new Int32Array([1, 2, 3, 4, 5]), 0, 3, 4);
// Int32Array [4, 2, 3, 4, 5]
					

规范

规范
ECMAScript (ECMA-262) The definition of 'Array.prototype.copyWithin' in that specification.

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
copyWithin	Chrome 45	Edge 12	Firefox 32	IE No	Opera 32	Safari 9	WebView Android 45	Chrome Android 45	Firefox Android 32	Opera Android 32	Safari iOS 9	Samsung Internet Android 5.0	nodejs 4.0.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• Array

元数据

• 最后修改： Aug 22, 2020

相关话题

1. 标准内置对象
2. Array
3. 特性
   1. Array.prototype.length
   2. Array.prototype[@@unscopables]
4. 方法
   1. Array.from()
   2. Array.isArray()
   3. Array.of()
   4. Array.prototype.concat()
   5. Array.prototype.copyWithin()
   6. Array.prototype.entries()
   7. Array.prototype.every()
   8. Array.prototype.fill()
   9. Array.prototype.filter()
   10. Array.prototype.find()
   11. Array.prototype.findIndex()
   12. Array.prototype.flat()
   13. Array.prototype.flatMap()
   14. Array.prototype.forEach()
   15. Array.prototype.includes()
   16. Array.prototype.indexOf()
   17. Array.prototype.join()
   18. Array.prototype.keys()
   19. Array.prototype.lastIndexOf()
   20. Array.prototype.map()
   21. Array.prototype.pop()
   22. Array.prototype.push()
   23. Array.prototype.reduce()
   24. Array.prototype.reduceRight()
   25. Array.prototype.reverse()
   26. Array.prototype.shift()
   27. Array.prototype.slice()
   28. Array.prototype.some()
   29. Array.prototype.sort()
   30. Array.prototype.splice()
   31. Array.prototype.toLocaleString()
   32. Array.prototype.toSource()
   33. Array.prototype.toString()
   34. Array.prototype.unshift()
   35. Array.prototype.values()
   36. Array.prototype[@@iterator]()
   37. get Array[@@species]
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()