Atomics.compareExchange()

这是一个实验中的功能
此功能某些浏览器尚在开发中，请参考浏览器兼容性表格以得到在不同浏览器中适合使用的前缀。由于该功能对应的标准文档可能被重新修订，所以在未来版本的浏览器中该功能的语法和行为可能随之改变。

Atomics.compareExchange() 静态方法会在数组的值与期望值相等的时候，将给定的替换值替换掉数组上的值，然后返回旧值。此原子操作保证在写上修改的值之前不会发生其他写操作。

语法

Atomics.compareExchange(typedArray, index, expectedValue, replacementValue)

参数

typedArray: 一个共享的整型 typed array。例如 Int8Array， Uint8Array， Int16Array， Uint16Array， Int32Array，或 Uint32Array。
index: typedArray 的索引。
expectedValue: 用于比较的值。
replacementValue: 将要替换上的值。

返回值

给定位置的旧值(typedArray[index]).

错误

假如 typedArray 不是允许的整型之一，则抛出 TypeError。
假如 typedArray 不是一个贡献的 typed array，则抛出 TypeError。
如果 index 超出了 typedArray 的边界，则抛出 RangeError。

示例

var sab = new SharedArrayBuffer(1024);
var ta = new Uint8Array(sab);
ta[0] = 7;

Atomics.compareExchange(ta, 0, 7, 12); // returns 7, the old value
Atomics.load(ta, 0); // 12

规范

Specification	Status	Comment
Unknown Atomics.compareExchange	Unknown	Initial definition.

浏览器支持

Update compatibility data on GitHub

	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
`compareExchange`	Chrome Full support 68 Full support 68 No support 60 — 63 Notes Notes Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This was a temporary removal while mitigations were put in place.	Edge No support 16 — 17 Notes No support 16 — 17 Notes Notes Support was removed to mitigate speculative execution side-channel attacks (Windows blog).	Firefox Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE No support No	Opera No support No	Safari No support 10.1 — ?	WebView Android No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	Chrome Android No support 60 — 63 Notes No support 60 — 63 Notes Notes Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	Firefox Android Full support 57 Notes Disabled Full support 57 Notes Disabled Notes Support was disabled by default to mitigate speculative execution side-channel attacks (Mozilla Security Blog). Disabled From version 57: this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. No support 55 — 57 No support 46 — 55 Disabled Disabled From version 46 until version 55 (exclusive): this feature is behind the `javascript.options.shared_memory` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No Notes No support No Notes Notes Chrome disabled `SharedArrayBuffer` on January 5, 2018 to help reduce the efficacy of speculative side-channel attacks. This is intended as a temporary measure until other mitigations are in place.	nodejs Full support 8.10.0

Legend

Full support: Full support
No support: No support
See implementation notes.: See implementation notes.
User must explicitly enable this feature.: User must explicitly enable this feature.

语法

参数

返回值

错误

示例

规范

浏览器支持

Legend

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