Name mangling rules allow creating JS objects with duplicate properties

[yawaramin]

According to the name mangling rules in #999, the following are valid in BuckleScript:

let a = [%bs.obj { x__int = 1; x__float = 1. }]
let b = [%bs.obj { x = 1; x__ = 1. }]

However they output JS output objects with duplicate properties:

var a = { x: 1, x: 1 };
var b = { x: 1, x: 1 };

However note that duplicate properties are not necessarily an error in JavaScript: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Duplicate_property_names

In ECMAScript 5 strict mode code, duplicate property names were considered a SyntaxError. With the introduction of computed property names making duplication possible at runtime, ECMAScript 2015 has removed this restriction.

[stale]

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