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  • `await null` to stay in the same tick?

`await null` to stay in the same tick?

# /#!/JoePea (9 years ago)

I'm not sure where's the best place to ask, but if I

await null

in an async function does that guarantee that the following code will execute immediately (control flow will not go anywhere else)?

# Mark S. Miller (9 years ago)

On Sun, Feb 7, 2016 at 1:38 PM, /#!/JoePea <joe at trusktr.io> wrote:

I'm not sure where's the best place to ask, but if I

await null

in an async function does that guarantee that the following code will execute immediately (control flow will not go anywhere else)?

Absolutely not. The continuation of an await always runs in another turn/job, i.e., it always starts with an empty stack. between the awaiting turn and the resumption at the await point, other jobs will interleave.

# Kris Kowal (9 years ago)

Await yields to the event loop unconditionally. This is useful for spreading CPU-bound work across multiple events. You can explicitly await conditionally.

if (guard) { await guard; }
# Mark S. Miller (9 years ago)

On Sun, Feb 7, 2016 at 1:51 PM, Kris Kowal <kris.kowal at cixar.com> wrote:

Await yields to the event loop unconditionally. This is useful for spreading CPU-bound work across multiple events. You can explicitly await conditionally.

if (guard) { await guard; }

Good example, thanks.

# /#!/JoePea (9 years ago)

Aah, good to know. With Babel this isn't the case, as await null doesn't defer, so I was doing await somethingThatMightBeNull to possibly defer, but if (somethingThatMightBeNull) await somethingThatMightBeNull will be full proof if Babel fixes that.

# /#!/JoePea (9 years ago)

(Or, maybe it's Facebook Regenerator's fault, not Babel's)

# Logan Smyth (9 years ago)

Joe, if you have a specific example, feel free to file an issue and I can take a look. From what I can see, babeljs.io/repl/#?experimental=true&evaluate=true&loose=false&spec=false&playground=false&code= (async function fn(){ console.log('start') Promise.resolve().then(() %3D> console.log('tick'))%3B%0A%20%20await%20null%3B%0A%20%20%0A%20%20console.log('end')%3B%0A%7D)()%3B would indicate that Babel always defers with Regenerator as well. Better to have this discussion elsewhere though.

# Isiah Meadows (9 years ago)

I believe Babel uses a modified Regenerator fork that only differs enough to work with Babel, and is otherwise kept as in sync as possible.