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Suppose some code does
// promise.js let p = new Promise(() => { /* ... */ }) export default p where Promise is an ES6 Promise. Suppose some other code has a reference only to p. How can that code tell if p is resolved or not?
// other.js import p from './promise.js' // console.log('p is resolved?', ______) Is there something we can fill in the blank with that would show true or false depending on whether the promise is resolved or not?
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You need to do something like this: import p from './promise. js' var isResolved = false; p. then(function() { isResolved = true; }); // ...
No. It is not safe to resolve/reject promise multiple times. It is basically a bug, that is hard to catch, becasue it can be not always reproducible.
Resolving a promise We check if the result is a promise or not. If it's a function, then call that function with value using doResolve() . If the result is a promise then it will be pushed to the deferreds array. You can find this logic in the finale function.
resolve() method "resolves" a given value to a Promise . If the value is a promise, that promise is returned; if the value is a thenable, Promise. resolve() will call the then() method with two callbacks it prepared; otherwise the returned promise will be fulfilled with the value.
Quoting the MDN documentation:
By design, the instant state and value of a promise cannot be inspected synchronously from code, without calling the then() method.
So, you need to call the .then method.
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The ES6 Promise constructor does not have a property that can tell you the state of the promise. You need to do something like this:
import p from './promise.js' var isResolved = false; p.then(function() { isResolved = true; }); // ... At some point in the future. console.log('p is resolved?', isResolved); There is an internal property called PromiseState but you can't access it. Here is the spec.
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