Promises and async/await
By the end of this lesson, you'll be able to:
- Explain what a Promise represents
- Use async/await syntax to work with asynchronous code
- Recognize that imperative Apex calls return Promises
Prerequisites: "Modules: Imports and Exports"
What Is a Promise?
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/await Syntax
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.
A Worked LWC Example
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.
Why This Matters in Real Projects
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.
Exercise
Convert this into an async function using await: function loadCases() { return getCases().then(result => console.log(result)); }
Show hint
async/await replaces .then() chains.
Exercise
Challenge: explain, as a comment, the three possible states of a Promise.
Show hint
One "in progress" state, and two "done" states.
Promises and async/await Quiz
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Summary
Every imperative Apex call in LWC returns a Promise — understanding what that means, and how async/await makes it readable, is required groundwork before Module 7 makes any sense.