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. Promises in JavaScript. Promise resolve() method: Promise.resolve() method in JS returns a Promise object that is resolved with a given value. First of all, a Promise is an object. Promise. // Parallel return Promise. A promise has 2 possible outcomes: it will either be kept when the time comes, or it won’t. 10 The above code shows a normal function which returns some value. 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. What value does the second promise resolve to? 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 new promise resolves when all listed promises are settled, and the array of their results becomes its result. It can also be the Promise or a thenable to resolve. The static Promise.resolve() function returns the Promise that is resolved. Running JavaScript Promises in parallel is as simple as calling Promise.all() with an array of Promises. 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()? Any of the three things can happend: If the value is a promise then promise is returned. Let us take a simple example. Promises and then function return values. The return type of Promise function will dictate how future chained then functions behave. Example. If the value has a “then” attached to the promise, then the returned promise will follow that “then” to till the final state. When we try to return the same value from an asynchronous callback function, we simply get nothing. Promise.all takes an array of promises (it technically can be any iterable, but is usually an array) and returns a new promise.. 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; } 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.. all ([task1, task2, task3,]). A promise is simply an object that represents a task that will be completed in the future. If there is a return statement in the handler function, it returns a fulfilled promise with that return value as the payload. It receives the return value of the first promise. The promise is resolved with the given value, or the promise passed as the value if the value was a promise object. This is happening at the bottom of handle(), The handler object carries around both an onResolved callback as well as a reference to resolve().There is more than one copy of resolve() floating around, each promise gets their own copy of this function, and a closure for it to run within. function run {const a = 10; return a;} run (); Output. This is also the same for promises in JavaScript. Putting the keyword async before a function tells the function to return a Promise. Promise.resolve(value); Parameters. This Promise resolves the value parameter. Although, as I mentioned, jQuery's Deferreds are a bit … unhelpful. 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