Promises and async/await

A Promise represents a value that will be available later, not immediately — it exists because operations like network calls take real time to complete. A Promise is always in one of three states: pending (still working), fulfilled (succeeded, with a result), or rejected (failed, with an error).

async function loadData() {
    const result = await somePromiseReturningFunction();
    console.log(result);
}

await pauses execution within that async function until the Promise resolves, letting you write asynchronous code that reads top-to-bottom like synchronous code — far cleaner than chaining .then() calls.

await on its own runs one Promise at a time — each await waits for its Promise to finish before the next line runs. When several independent operations don't depend on each other's results, waiting for them one after another wastes time. Promise.all runs them concurrently instead:

const [accounts, contacts] = await Promise.all([
    getAccounts(),
    getContacts(),
]);

Promise.all takes an array of Promises and returns a single Promise that resolves once every one of them has resolved, with an array of their results in the same order the Promises were given. If any one of them rejects, the whole Promise.all rejects immediately. This is the standard pattern whenever a component needs to fire off several independent Apex calls, or persist several independent record updates, without waiting for each one to finish before starting the next.

import getAccounts from '@salesforce/apex/AccountController.getAccounts';

async handleLoadClick() {
    try {
        const accounts = await getAccounts();
        this.accounts = accounts;
    } catch (error) {
        this.error = error;
    }
}

Every imperative Apex call (as opposed to @wire, covered in Module 7) returns a Promise — this is exactly why async/await matters for LWC specifically, not just as general JavaScript trivia.

Without understanding Promises, imperative Apex calls look like mysterious, hard-to-predict code. With this foundation in place, Module 7's Apex integration lessons will make immediate sense rather than feeling like new, unrelated syntax.