JavaScript Promise catch() method is called whenever a promise is rejected. This method itself returns a promise so it can also be used to chain promises. This method is used for error handling. This method is mainly used after .then to chain a promise and handle reject condition. This method internally calls .then with undefined and rejected conditions as arguments.Â
Syntax:
catch(()=>{})
Parameter: This method takes a callback function that decides what action to perform when the promise is rejected
Return Type: This method returns a promise which is in the pending state even if the previous promise is finished.
Example 1: This example uses the catch method to handle the reject condition of a promise.
Javascript
let prom1 = new Promise((resolve, reject) => {Â Â Â Â reject("Failure");})Â Â Â Â .then(e => { console.log("Hello Successful") })Â Â Â Â .catch((e) => { console.log(e) }) |
Output: Since the promise returns a reject it moves to the catch method where the rejected value is received and printed on the console.
Failure
Example 2: This example specifies a condition where the catch method fails to catch an error.
Javascript
let prom1 = new Promise((resolve, reject) => {Â Â Â Â setTimeout(() => { throw new Error("Failure") }, 1000);})Â
prom1.catch((e) => { console.log(e) }) |
Output: Normally this error should be caught by the catch block but since the error is thrown by an asynchronous function the catch block fails to handle it.
Â
Example 3: This method explains the condition when the catch method will not be called.
Javascript
let x = 10;let y = 10;let prom1 = new Promise((resolve, reject) => {Â Â Â Â if (x == y) {Â Â Â Â Â Â Â Â resolve("Equal Values")Â Â Â Â } else {Â Â Â Â Â Â Â Â reject("Unequal Values")Â Â Â Â }})Â
prom1.then((e) => { console.log(e) });prom1.catch((e) => { console.log(e) }) |
Output: The catch method is not called as the promise is resolved so only then the method is called.
Equal Values
Supported Browsers:Â
- Google Chrome
- Mozilla FirefoxÂ
- OperaÂ
- SafariÂ
- EdgeÂ
We have a complete list of Javascript Promise methods, to check those please go through the Javascript Promise Reference article.
