Error.prototype.toString()
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The toString() method of Error instances returns a string representing this error.
Syntax
js
toString()
Parameters
None.
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:
js
Error.prototype.toString = function () {
if (
this === null ||
(typeof this !== "object" && typeof this !== "function")
) {
throw new TypeError();
}
let name = this.name;
name = name === undefined ? "Error" : `${name}`;
let msg = this.message;
msg = msg === undefined ? "" : `${msg}`;
if (name === "") {
return msg;
}
if (msg === "") {
return name;
}
return `${name}: ${msg}`;
};
Examples
Using toString()
js
const e1 = new Error("fatal error");
console.log(e1.toString()); // "Error: fatal error"
const e2 = new Error("fatal error");
e2.name = undefined;
console.log(e2.toString()); // "Error: fatal error"
const e3 = new Error("fatal error");
e3.name = "";
console.log(e3.toString()); // "fatal error"
const e4 = new Error("fatal error");
e4.name = "";
e4.message = undefined;
console.log(e4.toString()); // ""
const e5 = new Error("fatal error");
e5.name = "hello";
e5.message = undefined;
console.log(e5.toString()); // "hello"
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-error.prototype.tostring |