Disallows unnecessary 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.

Rule Details

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

The following patterns are considered warnings:

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

The following patterns are not warnings:

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().

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.

Further Reading

async function on MDN

Version

This rule was introduced in ESLint 3.10.0.

Resources

• Rule source
• Documentation source