The JavaScript promises API will treat anything with a then() method as promise-like (or thenable in promise-speak sigh), so if you use a library that returns a Q promise, that's fine, it'll play nice with the new JavaScript promises. The Promise.all() is a static method (part of Promise API) that executes many promises in parallel, and waits until all of them are settled. If you return a Promise then the next chained then function will execute when the Promise that you returned is resolved.. Promise.resolve('foo'). The promise is resolved with the given value, or the promise passed as the value if the value was a promise object. Promises in JavaScript. Any of the three things can happend: If the value is a promise then promise is returned. If the value has a “then” attached to the promise, then the returned promise will follow that “then” to till the final state. Example. If there is a return statement in the handler function, it returns a fulfilled promise with that return value as the payload. all ([task1, task2, task3,]). Promise resolve() method: Promise.resolve() method in JS returns a Promise object that is resolved with a given value. The return type of Promise function will dictate how future chained then functions behave. For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3]: The static Promise.resolve() function returns the Promise that is resolved. The new promise resolves when all listed promises are settled, and the array of their results becomes its result. 10 The above code shows a normal function which returns some value. Return a Default Value with Promises Using catch By David Walsh on December 23, 2020 Last week I tweeted all of you looking for your best JavaScript Array and Promise tricks , and as always, it didn't disappoint -- I learned quite a bit! Here the first .then shows 1 and returns new Promise(…) in the line (*).After one second it resolves, and the result (the argument of resolve, here it’s result * 2) is passed on to handler of the second .then.That handler is in the line (**), it shows 2 and does the same thing.. Although, as I mentioned, jQuery's Deferreds are a bit … unhelpful. This is also the same for promises in JavaScript. Promise. When we define a promise in JavaScript, it will be resolved when the time comes, or it will get rejected. But sometimes you need to run then in sequential order. function run {const a = 10; return a;} run (); Output. What value does the second promise resolve to? Promises and then function return values. What then? JavaScript promises are one of the most popular ways of writing asynchronous functions that return a single value on completion or failure of the operation.. What is Promise.all()? When we try to return the same value from an asynchronous callback function, we simply get nothing. Running JavaScript Promises in parallel is as simple as calling Promise.all() with an array of Promises. A promise is simply an object that represents a task that will be completed in the future. So how do we do that? Promise.resolve(value); Parameters. Putting the keyword async before a function tells the function to return a Promise. then (arrayOfResults => {// Do something with all results}); It can also be the Promise or a thenable to resolve. If the code returns something that is not a Promise, then JavaScript automatically wraps it into a resolved promise with that value e.g when it returns an AsyncFunction object: async function oddNumber() { return 7; } Let us take a simple example. It receives the return value of the first promise. 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