In JavaScript, a Promise is an object representing the eventual completion or failure of an asynchronous operation.
Promise have 3 states:
1.Pending - Initial state, (waiting for response)
2.Fulfill- Operation completed successfully (resolve() was called)
3.Rejected - Operation failed (reject() was called)
Syntax for promise:
const promise = new Promise((resolve, reject) => {
if (success) {
resolve(result);
} else {
reject(error);
}
});
- resolve: Call this when the task is successful
- reject: Call this when the task fails
Example:
<script>
function login() {
return new Promise((resolve, reject) => {
let password = true;
if (password) {
resolve();
} else {
reject();
}
})
}
login()
.then(() => console.log("successfully login..."))
.catch(() => console.log("invalid password..."))
</script>
Output:
