js-promise-timeout.js

/**
 * The implementation of this is heavily inspired from the article:
 * https://ourcodeworld.com/articles/read/1544/how-to-implement-a-timeout-for-javascript-promises
 */


/**
 * Waits the execution till passed milliseconds.
 * 
 * @param {*} milliseconds 
 * @returns 
 */
const waitTill = (milliseconds) => {
		return new Promise((resolve) => {
			setTimeout(resolve, milliseconds);
		});
	};


/**
 * Sample function to demonstrate a long process.
 *  
 * @returns 
 */
async function myLongProcess () {
	await waitTill(10000);
	console.log("myLongProcess execution completed");
	return "Result from myLongProcess";
}

/**
 * Accepts a promise and a timeout in milliseconds.
 * If the promise is not get resolved/rejected in the specified
 * timeout, it returns a rejected promise "timeout".
 * 
 * @param {*} promise 
 * @param {*} timeoutInMilliseconds 
 * @returns 
 */
function promiseTimeout (promise, timeoutInMilliseconds){
    return Promise.race([
        promise, 
        new Promise(function(resolve, reject){
            setTimeout(function() {
                reject("timeout");
            }, timeoutInMilliseconds);
        })
    ]);
}

/**
 * Test ground
 */
async function main() {
	console.log("Program started....")

	/**
	 * Please note that, we need to take the promise of the long running
	 * function for passing it to the promiseTimeout. So, don't make an
	 * await call here for preserving the Promise.
	 */
	const myLongProcessPromise = myLongProcess();
	

	try {
		const TIMEOUT = 5000;
		/**
		 * Try changing the value of TIMEOUT to something different to see
		 * the difference. Our long running function need 10000 ms to finish
		 * it's execution. Thus, any timeout value less than that will result
		 * in killing the execution and hitting the timeout.
		 */
		const result = await promiseTimeout(myLongProcessPromise, TIMEOUT);


		console.log("Result :>> ", result);
	} catch (error) {
		/**
		 * If the error is thrown from the timeout Promise, it can be equated
		 * to "timeout". Else it will be some different error and can be handled
		 * in the else block appropriately.
		 */
		if (error === "timeout") {
			console.log("Error :>> timeout error :>> ", error);
		} else {
			console.log("Error :>>", error);
		}
	}


	console.log("Program finished")
}

main();