JavaScript promise reject() Method

The Promise.reject() method is used to return a rejected Promise object with a given reason for rejection. It is used for debugging purposes and selective error-catching. The catch() method can be used for logging the output of the reject() method to the console that is catch() method acts as a career that carries the rejected message from the Promise.reject() method and displays that in the user's console.

Syntax:

Promise.reject(reason);

Parameter:

This method accepts a single parameter as mentioned above and described below:

• reason: It is the reason for which the promise is rejected.

Return value:

It returns the rejected promise with the given reason, either specified by the user or via the backend.

Example 1: In this example, a Promise is instantly rejected with the reason "I am a reason of error." The catch() method logs the error to the console, showcasing a concise error-handling mechanism using JavaScript Promises.

// Initialize a promise variable and
// use the reject() method with a
// reason as a parameter
let promise = Promise.reject("I am a reason of error");

// Catch the promise and pass the
// function for logging the error in console
promise.catch(function (error) {
    console.log(error);
});

I am a reason of error

Example 2: In this example, a Promise in the main function simulates an error using a timeout and explicitly rejects it. The catch() method handles the rejection, logging "rejected the promise, something wrong happened" if an error occurs. This showcases asynchronous error handling with Promises in JavaScript.

function main() {
    return new Promise(function (resolve, reject) {
        setTimeout(() => {
            // This is the error which is handled
            // according to network requests
            const error = true;
            reject();
        }, 2000);
    });
}
main().catch(function () {
    // Only executed if rejects the promise
    console.log("rejected the promise, something wrong happened");
});

Output:

rejected the promise, something wrong happened

Example 3: In this example, the main function creates a Promise where the condition checks if num is greater than 50. If true, the Promise is rejected. The catch() method handles the rejection, logging "Not greater than 100" to the console. This demonstrates a concise asynchronous error check using Promises in JavaScript.

function main() {
    return new Promise(function (resolve, reject) {
        num = 100;
        if (num > 50) {
            reject();
        }
    });
}
main().catch(function () {
    // Only executed if rejects the promise
    console.log("Not greater than 100");
});

Not greater than 100

Supported Browsers:

• Google Chrome 32 and above
• Edge 12 and above
• Firefox 29 and above
• Opera 19 and above
• Safari 8 and above