Emitter: Static class property "name" causes TypeError due to Function.name being readonly

[about-code]

TypeScript Version: 1.8.10

Consider the following class definition with a static property name:

class Foo {
     static name() {
         return "Hello World";
     }
     constructor() {}
}

The TS emitter output for this is:

var Foo = (function () {
    function Foo() {
    }
    Foo.name = function () {
        return "Hello World";
    };
    return Foo;
}());

However, at least in Chrome and Firefox a function's name property is readonly for ordinary functions causing the assignment of the static function name to be ignored / causing a TypeError in strict mode.

The TS example above is also valid ES 2015 so I've tested it without transpilation in a current version of Chromium (v51.0.2704.79). Interestingly, while we can not change the name property of ordinary functions in Chromium we can still do the following for the constructor function once a static name property is present:

class Foo {
   static name() {
        return "Hello World";
   }
   constructor {}
}
Foo.name = "Hello World"
console.log(Foo.name); // logs "Hello World"

So the name property of the constructor function is no longer read-only. Based on this I assume Chromium internally does something like

Expected behavior:

var Foo = (function () {
    function Foo() {
    }
    Object.defineProperty(Foo, "name", { writable: true; });  // <= required for static class property *name*
    Foo.name = function () {
        return "Hello World";
    };
    return Foo;
}());

So a static class property name requires the name property to be made writable: true first. Unfortunately, Object.defineProperty is only available since ES 5 so static properties could become problematic for a compiler target of es3.

Therefore you might also want to note, that section 9.11.2 of ES2015 spec states that the ES interpreter must not set the name property, if a function does have an OwnProperty name. So the spec does seem to take custom values for Function.name into account which is why I consider a default configuration of writable: false for Function.name being problematic. It would certainly be better if browser vendors could agree here on making Function.name writable: true by default.

[about-code]

Note: it seems there have been some issues with

Object.defineProperty(Foo, "name", { writable: true; });

in the past with older versions of Chrome, due to older Chromes having set configurability of Function.name to false. See comment of @alexeagle and @rbuckton regarding issue #2836.

[mhegazy]

Duplicate of #442