blog

Bez Hermoso, Software Engineer @ Square

More Pro-tips...

Create custom Javascript errors

29 Feb 2016

When building complex Javascript applications for the browser or server, sooner or later you’ll find the need to create custom error objects especially when implementing fail-safes, error handling (i.e. catching specific errors in a Promise chain), etc.

Here is a short snippet of how to create a custom Error sub-type in Javascript:

function CustomError(message) {
  this.message = message || "You shouldn't have done that.";
  this.stack = (new Error()).stack;
}
CustomError.prototype = Object.create(Error.prototype);
CustomError.prototype.constructor = CustomError;
CustomError.prototype.name = "CustomError";

It’s more succinct in ES6:

class CustomError extends Error {
    constructor(message) {
        super(message);
        this.message = message || "You shouldn't have done that.";
        this.name = this.constructor.name;
        this.stack = (new Error()).stack;
    }
}