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avoid Array.from and Reflect #9

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avoid Array.from and Reflect #9

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cdcedaa
avoid Array.from and Reflect
graingert May 8, 2017
aafe8fe
consistent use of get/setPrototypeOf polyfill
May 8, 2017
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16 changes: 9 additions & 7 deletions src/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,11 +6,17 @@ import template from 'babel-template';
*/
const buildHelper = template(`
function HELPER(cls){
var setPrototypeOf = Object.setPrototypeOf || (function setPrototypeOf(a, b) {
a.__proto__ = b;
});
var getPrototypeOf = Object.getPrototypeOf || (function getPrototypeOf(a)) {
return a.__proto__;
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I can't imagine a case where getPrototypeOf doesn't exist but __proto__ does. getPrototypeOf is from ES5, so it either exists, or there's no way to polyfill it AFAIK.

});
function ExtendableBuiltin(){
// Not passing "newTarget" because core-js would fall back to non-exotic
// object creation.
var instance = Reflect.construct(cls, Array.from(arguments));
Object.setPrototypeOf(instance, Object.getPrototypeOf(this));
var instance = new (Function.prototype.bind.apply(cls, arguments))();
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The general concern with approaches like this is that .bind is known to be slow. Most things optimize this like statements like https://github.com/zloirock/core-js/blob/master/modules/es6.reflect.construct.js#L29, so larger code like that was what I was trying to avoid.

setPrototypeOf(instance, getPrototypeOf(this));
return instance;
}
ExtendableBuiltin.prototype = Object.create(cls.prototype, {
Expand All @@ -21,12 +27,8 @@ const buildHelper = template(`
configurable: true,
},
});
if (Object.setPrototypeOf){
Object.setPrototypeOf(ExtendableBuiltin, cls);
} else {
ExtendableBuiltin.__proto__ = cls;
}

setPrototypeOf(ExtendableBuiltin, cls);
return ExtendableBuiltin;
}
`);
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