Stage: 1
Champions:
- Ashley Claymore (@acutmore)
- Jordan Harband (@ljharb)
- Chris de Almeida (@ctcpip)
- TBC: Rick Waldron (@rwaldron)
Authors:
- Alexander J. Vincent (@ajvincent)
- Ashley Claymore (@acutmore)
await
on individual properties creates a waterfall, rather than running requests in parallel:
const obj = {
shape: await getShape(),
color: await getColor(),
mass: await getMass(),
};
Promise.all
helps, but is based on order, rather than names, which could lead to mixups:
const [
color,
shape,
mass,
] = await Promise.all([
getShape(),
getColor(),
getMass(),
]);
Solutions using existing syntax can be verbose and pollute the number of variables in scope:
const shapeRequest = getShape();
const colorRequest = getColor();
const massRequest = getMass();
const shape = await shapeRequest;
const color = await colorRequest;
const mass = await massRequest;
const {
shape,
color,
mass,
} = await Promise.ownProperties({
shape: getShape(),
color: getColor(),
mass: getMass(),
});
const {
shape,
color,
mass,
} = await Promise.fromEntries(Object.entries({
shape: getShape(),
color: getColor(),
mass: getMass(),
}));
http://bluebirdjs.com/docs/api/promise.props.html
https://github.com/slorber/combine-promises
https://github.com/sindresorhus/p-props
None.
None.
Q: Why not a deep-copy option?
A: Deep copy traditionally has been left out of JavaScript for a number of reasons. While a recursive promise walking API might be possible, combining it with this feels overcomplicated and unlikely to pass TC39's smell tests.
Q: Why not all keys?
A: This implies walking the prototype chain. Note this proposal would have been Promise.allProperties()
originally, but that naming confuses what the polyfill does above with that intended use case. Plus, if a prototype has promises on it, then how would we safely construct the prototype of the resulting object? Going down the prototype chain opens a can of worms.
Q: What about symbol keys?
A: We haven't really talked about them yet. That said, Object.entries()
, for better or for worse, only considers string keys.