require-atomic-updates

禁止由于使用 await 或 yield 而可能导致竞争条件的分配

在编写异步代码时，可能会产生微妙的竞争条件错误。考虑以下示例：

let totalLength = 0;

async function addLengthOfSinglePage(pageNum) {
  totalLength += await getPageLength(pageNum);
}

Promise.all([addLengthOfSinglePage(1), addLengthOfSinglePage(2)]).then(() => {
  console.log('The combined length of both pages is', totalLength);
});

这段代码看起来将调用 getPageLength(1) 和 getPageLength(2) 的结果相加，但实际上 totalLength 的最终值只是两页之一的长度。错误在语句 totalLength += await getPageLength(pageNum); 中。该语句首先读取 totalLength 的初始值，然后调用 getPageLength(pageNum) 并等待该 Promise 完成。最后，它将 totalLength 的值设置为 await getPageLength(pageNum) 和 totalLength 的初始值之和。如果在 getPageLength(pageNum) Promise 未决期间在单独的函数调用中更新了 totalLength 变量，则该更新将丢失，因为新值被覆盖而未被读取。

解决此问题的一种方法是确保在更新 totalLength 的同时读取它，如下所示：

async function addLengthOfSinglePage(pageNum) {
  const lengthOfThisPage = await getPageLength(pageNum);

  totalLength += lengthOfThisPage;
}

另一种解决方案是完全避免使用可变变量引用：

Promise.all([getPageLength(1), getPageLength(2)]).then(pageLengths => {
  const totalLength = pageLengths.reduce((accumulator, length) => accumulator + length, 0);

  console.log('The combined length of both pages is', totalLength);
});

规则详情

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变量

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  1. 变量被读取。
  2. yield 或 await 暂停该功能。
  3. 函数恢复后，从第 1 步开始为变量赋值。

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/* eslint require-atomic-updates: error */

let result;

async function foo() {
    result += await something;
}

async function bar() {
    result = result + await something;
}

async function baz() {
    result = result + doSomething(await somethingElse);
}

async function qux() {
    if (!result) {
        result = await initialize();
    }
}

function* generator() {
    result += yield;
}

x8vS/D2xVZSiiHLs1PwUl6/TVEXV0uticb8dGcMm9rxiwxh8yRqnjwkHP0i+2Pam

/* eslint require-atomic-updates: error */

let result;

async function foobar() {
    result = await something + result;
}

async function baz() {
    const tmp = doSomething(await somethingElse);
    result += tmp;
}

async function qux() {
    if (!result) {
        const tmp = await initialize();
        if (!result) {
            result = tmp;
        }
    }
}

async function quux() {
    let localVariable = 0;
    localVariable += await something;
}

function* generator() {
    result = (yield) + result;
}

属性

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  1. 读取变量或对象属性。
  2. yield 或 await 暂停该功能。
  3. 函数恢复后，将值分配给属性。

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/* eslint require-atomic-updates: error */

async function foo(obj) {
    if (!obj.done) {
        obj.something = await getSomething();
    }
}

x8vS/D2xVZSiiHLs1PwUl6/TVEXV0uticb8dGcMm9rxiwxh8yRqnjwkHP0i+2Pam

/* eslint require-atomic-updates: error */

async function foo(obj) {
    if (!obj.done) {
        const tmp = await getSomething();
        if (!obj.done) {
            obj.something = tmp;
        }
    }
}

选项

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allowProperties

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/* eslint require-atomic-updates: ["error", { "allowProperties": true }] */

async function foo(obj) {
    if (!obj.done) {
        obj.something = await getSomething();
    }
}

何时不使用

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