Disallows unnecessary return await (no-return-await)

禁用不必要的 return await (no-return-await)

Inside an async function, return await is seldom useful. Since the return value of an async function is always wrapped in Promise.resolve, return await doesn’t actually do anything except add extra time before the overarching Promise resolves or rejects. The only valid exception is if return await is used in a try/catch statement to catch errors from another Promise-based function.

在 async function， return await 很少有用。因为 async function 的返回值总是封装在 Promise.resolve，return await 实际上并没有做任何事情，只是在 Promise resolve 或 reject 之前增加了额外的时间。唯一有效是，如果 try/catch 语句中使用 return await 来捕获另一个基于 Promise 的函数的错误，则会出现异常。

Rule Details

This rule aims to prevent a likely common performance hazard due to a lack of understanding of the semantics of async function.

该规则旨在防止由于缺乏对 async function 语法的理解而造成的常见的性能风险。

Examples of incorrect code for this rule:

错误 代码示例：

async function foo() {
    return await bar();
}

Examples of correct code for this rule:

正确的 代码示例：

async function foo() {
    return bar();
}

async function foo() {
    await bar();
    return;
}

async function foo() {
    const x = await bar();
    return x;
}

async function foo() {
    try {
        return await bar();
    } catch (error) {}
}

In the last example the await is necessary to be able to catch errors thrown from bar().

在最后一个例子中，await 是必须的，可以捕获从 bar() 抛出的错误。

When Not To Use It

If you want to use await to denote a value that is a thenable, even when it is not necessary; or if you do not want the performance benefit of avoiding return await, you can turn off this rule.

如果你使用 await 来表示一个 thenable 的值，即使是非必要的；或，如果你不想要因避免 return await 而带来的性能好处，你可以关闭此规则。

Further Reading

async function on MDN

Version

This rule was introduced in ESLint 3.10.0.

该规则在 ESLint 3.10.0 中被引入。

Resources