Custom errors in JavaScript

illegal-argument-error.js

function IllegalArgumentError(message) {
    Error.call(this, message);
    this.name = 'IllegalArgumentError';
}

IllegalArgumentError.prototype = new Error();
IllegalArgumentError.prototype.constructor = IllegalArgumentError;

Custom errors created following this pattern will behave exactly like the built-in errors. For example, when thrown, IllegalArgumentError will print stack trace exactly how throwing the built-in Error would.

Three rules of proper prototypal inheritance in JavaScript:

1. Remember to call super constructor function (line #2)
2. Set prototype to instance of parent constructor (line #6)
3. "Fix" the constructor (line #7).