Promise

`Promise.prototype.catch`

Attaches a rejection handler callback to the promise and returns a new Promise resolving to the return value of the callback if called, or the original fulfilled value if the promise is resolved

Syntax

JavaScript

promise.catch(onRejected)

Parameters

Parameter	Type	Description
onRejected	(reason: any) => T \| PromiseLike<T>	Callback for when the promise is rejected

Return Value

A new Promise

Examples

Basic Usage

fetch('/api/data')
  .then(r => r.json())
  .catch(err => console.error('Failed:', err));

Practical Example

async function safeParse(json: string) {
  return Promise.resolve(json)
    .then(JSON.parse)
    .catch(() => null);
}
console.log(await safeParse('invalid')); // null

Advanced Usage

Promise.reject(new Error('oops'))
  .catch(err => {
    console.log(err.message); // 'oops'
    return 'recovered';
  })
  .then(val => console.log(val)); // 'recovered'

Understanding Promise.prototype.catch

The Promise.prototype.catch method in JavaScript attaches a rejection handler callback to the promise and returns a new Promise resolving to the return value of the callback if called, or the original fulfilled value if the promise is resolved. It belongs to the Promise object and is one of the most widely used methods for working with promise values in modern JavaScript and TypeScript applications.

The method signature is promise.catch(onRejected). It accepts 1 parameter: onRejected. When called, it returns a new promise. Understanding when and how to use catch() helps you write more expressive, readable code.

Common use cases for Promise.prototype.catch include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like promise-then, promise-finally, promise-reject, enabling you to chain operations together for complex data manipulation pipelines.

Browser support for Promise.prototype.catch is excellent across all modern browsers including Chrome, Firefox, Safari, and Edge. It is also fully supported in Node.js and Deno. For older environments, transpilation with Babel or a polyfill may be needed.