Creating a (ES6) promise without starting to resolve it

by

Good question!

The resolver passed to the promise constructor intentionally runs synchronous in order to support this use case:

var deferreds = [];
var p = new Promise(function(resolve, reject){
    deferreds.push({resolve: resolve, reject: reject});
});

Then, at some later point in time:

 deferreds[0].resolve("Hello"); // resolve the promise with "Hello"

The reason the promise constructor is given is that:

  • Typically (but not always) resolution logic is bound to the creation.
  • The promise constructor is throw safe and converts exceptions to rejections.

Sometimes it doesn’t fit and for that it the resolver runs synchronously. Here is related reading on the topic.

More Related Contents:

  1. How do I access previous promise results in a .then() chain?
  2. Wait until all promises complete even if some rejected
  3. Can I fire and forget a promise in nodejs (ES7)?
  4. Promise.all: Order of resolved values
  5. How can I fetch an array of URLs with Promise.all?
  6. Is the Promise constructor callback executed asynchronously?
  7. Is Node.js native Promise.all processing in parallel or sequentially?
  8. What is the order of execution in JavaScript promises?
  9. How can I synchronously determine a JavaScript Promise’s state?
  10. When is the body of a Promise executed?
  11. Do I need to return after early resolve/reject?
  12. ES6 Promise.all() error handle – Is .settle() needed? [duplicate]
  13. Resolve Javascript Promise outside the Promise constructor scope
  14. multiple, sequential fetch() Promise
  15. How to check if an object is a Promise?
  16. Should a Promise.reject message be wrapped in Error?
  17. Why can I not throw inside a Promise.catch handler?
  18. What do double brackets mean in javascript and how to access them
  19. What is the best general practice to timeout a function in promise [closed]
  20. When would someone need to create a deferred?
  21. Why does the Promise object block rendering?
  22. How to extract data out of a Promise
  23. Promise and Promise.all(array) executed before array fulfilled [duplicate]
  24. Node.js: When to use Promises vs Callbacks
  25. Are JavaScript forever-pending promises bad?
  26. Why does javascript ES6 Promises continue execution after a resolve?
  27. Why does JavaScript Promise then handler run after other code?
  28. Promise.all is returning an array of undefined and resolves before being done
  29. Weird behavior with Promise throwing “Unhandled promise rejection” error
  30. Promise.resolve().then vs setImmediate vs nextTick

Leave a Comment