Bug 203478 – Poor Async/Await Syntax Error Message

• Component: JavaScriptCore
• Status: NEW

[Ezekiel Elin]

The `await` keyword can only be used in functions marked `async.` When one tries to use it in a function not marked as such, evaluation fails with the error:

    function b() {
      const x = await "Hello";
    }

    SyntaxError: Unexpected string literal "Hello". Expected ';' after variable declaration.

This should instead say something like (copied from Firefox):

    SyntaxError: await is only valid in async functions and async generators

The correct code is:

    async function b() {
      const x = await "Hello";
    }

[Ross Kirsling]

That would be a more helpful error message indeed.

Note that the reason for the current error message is that `await` is a valid *identifier* just when we're *not* in an async function.

So this is all perfectly valid code (for web compatibility reasons):

    const await = "Hello";
    const x = await;

    function f(await) { console.log(await); }

[Radar WebKit Bug Importer]

<rdar://problem/91439731>