Error.prototype.toString()

The toString() method returns a string representing the specified Error object.

Syntax

toString()

Return value

A string representing the specified Error object.

Description

The Error object overrides the Object.prototype.toString() method inherited by all objects. Its semantics are as follows (assuming Object and String have their original values):

Error.prototype.toString = function() {
  'use strict';

  var obj = Object(this);
  if (obj !== this) {
    throw new TypeError();
  }

  var name = this.name;
  name = (name === undefined) ? 'Error' : String(name);

  var msg = this.message;
  msg = (msg === undefined) ? '' : String(msg);

  if (name === '') {
    return msg;
  }
  if (msg === '') {
    return name;
  }

  return name + ': ' + msg;
};

Examples

Using toString()

var e1 = new Error('fatal error');
console.log(e1.toString()); // 'Error: fatal error'

var e2 = new Error('fatal error');
e2.name = undefined;
console.log(e2.toString()); // 'Error: fatal error'

var e3 = new Error('fatal error');
e3.name = '';
console.log(e3.toString()); // 'fatal error'

var e4 = new Error('fatal error');
e4.name = '';
e4.message = undefined;
console.log(e4.toString()); // ''

var e5 = new Error('fatal error');
e5.name = 'hello';
e5.message = undefined;
console.log(e5.toString()); // 'hello'

Specifications

Specification
ECMAScript Language Specification # sec-error.prototype.tostring

Browser compatibility

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