javascript - Why are generator methods constructors? -

methods when declared methods (using es6 enhanced object literals or classes) not constructors / not have prototype chain.

but generators when declared via method syntax, have prototype chain , constructors.

take following example - (requires v8)

'use strict'; class x {   *a() { this.b() }   b() { print('class method'); } } let = new x(); i.a.prototype.b = function() { print('generator method'); }; i.a().next(); (new i.a()).next(); 

outputs,

class method generator method 

while adding prototypes i.b, , calling new i.b() throw error because i.b not constructor, i'm able new i.a(), , this inside *a gets different context.

• why difference exist?
• what use case having prototype in generators defined methods?

definitely odd quirk of es2015 spec. tc39 had long discussion back in july, , decided make generators non-newable.

the official change spec landed last month, , while there little concern breaking things, v8 , spidermonkey implementors in favor of going forward, expect see stop working (and in fact, throws typeerror in firefox nightly).