Function.prototype.bind about polyfill-service

[jonathantneal]

After testing native bind against our polyfill and the MDN polyfill, I’m afraid I can’t replicate the issue you are having.

Native:
new (String.bind('test')) === new (String.bind('test')) // returns false

Our polyfill:
new (String.bind('test')) === new (String.bind('test')) // returns false

MDN Polyfill:
new (String.bind('test')) === new (String.bind('test')) // returns false

Native:
new (function (e) { console.log(e) }.bind(null, 'test')) // logs "test", returns Object {}

Our polyfill:
new (function (e) { console.log(e) }.bind(null, 'test')) // logs "test", returns bound {}

MDN Polyfill:
new (function (e) { console.log(e) }.bind(null, 'test')) // logs "test", returns fBound {}

Would you provide more details and perhaps a test?

[jdalton]

Your bind will also error when attempting to bind a native method. This is because native methods don't have a prototype property so your bound function gets a prototype of undefined which then throws an error when you do the this instanceof Constructor check.

[abozhilov]

Sorry about my examples. As I told you built-in constructors have overloaded behavior depends how they are called .

new String('test'); //string object
String('test'); //primitive string value

Your bind implementation doesn't handle that.

String(new (String.bind(null, 'test'))); //Native bind returns 'test'

Your bind fails with error since String#toString is not generic.

[matthewwithanm]

I just bumped into the issue described by @jdalton. Here's the exact message for reference:

Uncaught TypeError: Function has non-object prototype 'undefined' in instanceof check 

And here's code to cause it:

RegExp.prototype.test.bind(/a/)('a');

[samgiles]

Added test case in https://github.com/Financial-Times/polyfill-service/blob/functionbind_test/polyfills/Function.prototype.bind/tests.js

[triblondon]

Lots of issues reported with our bind implementation: ref #313 and #261