Is there anything in the spec that defines a toString() method for classes?

For example, let's say I define this class:

class Foo {
  constructor() {
    console.log('hello');
  }
}

If I called Foo.toString(), I'm not sure if I'll get:

class Foo {
  constructor() {
    console.log('hello');
  }
}

Or perhaps the constructor function, anonymous:

function() {
  console.log('hello');
}

Or maybe the constructor function, but it's named:

function Foo() {
  console.log('hello');
}

Or maybe just the class name:

Foo

Is there anything in the spec that defines a toString() method for classes?

For example, let's say I define this class:

class Foo {
  constructor() {
    console.log('hello');
  }
}

If I called Foo.toString(), I'm not sure if I'll get:

class Foo {
  constructor() {
    console.log('hello');
  }
}

Or perhaps the constructor function, anonymous:

function() {
  console.log('hello');
}

Or maybe the constructor function, but it's named:

function Foo() {
  console.log('hello');
}

Or maybe just the class name:

Foo

• javascript
• ecmascript-6

• 4 Have you tried running the code? – chead23 Commented Jan 9, 2015 at 17:02
• 4 Have you tried reading the spec? – Barmar Commented Jan 9, 2015 at 17:02
• I've read the spec (people.mozilla/~jorendorff/…) but there's nothing there about it. But maybe I didn't read it fully enough (toString might be defined elsewhere?), or maybe classes act like their underlying constructor function? Running the code wouldn't matter if it's not in the spec, because I can theoretically create an ES6 runtime on my own that does whatever the heck I feel like when toString() is called on a class. – Daniel Weiner Commented Jan 9, 2015 at 17:07
• Re-read the spec and I found what Felix Kling is talking about. Thanks! – Daniel Weiner Commented Jan 9, 2015 at 17:22

1 Answer 1

Actually in ES6 "class" is just a function. So to understand how toString behave for so-called "classes" you must look at toString() specification for function. It says:

The string representation must have the syntax of a FunctionDeclaration FunctionExpression, GeneratorDeclaration, GeneratorExpession, ClassDeclaration, ClassExpression, ArrowFunction, MethodDefinition, or GeneratorMethod depending upon the actual characteristics of the object.

So for example 'toString()' for the next class:

class Foo {
    // some very important constructor
    constructor() {
       // body
    }

    /**
     * Getting some name
     */
    getName() {
    }
}

toString() method will return string:

Foo.toString() === `class Foo {
    // some very important constructor
    constructor() {
       // body
    }

    /**
     * Getting some name
     */
    getName() {
    }
}`;

PS

1. Pay attention that I wrote the string in back quotes ``. I did it to specify multiline string.
2. Also spec says that use and placement of white space, line terminators, and semicolons within the representation String is implementation-dependent. But now all JS realizations remains them unchanged.
3. You can test example in Chrome Canary, which now supports ES6 classes.