conversion from loop body to function munges keyword object properties

[sciolizer]

TypeScript Version: 2.1.5

Code

type MyType = {
    arguments: Array<string>
}

function myFunction(myType: MyType) {
    for (let i = 0; i < 10; i++) {
        console.log(myType.arguments[i]);

        // create closure so that tsc will turn loop body into function
        const x = 5;
        [1, 2, 3].forEach(function(j) {
            console.log(x);
        })
    }
}

export { myFunction };

Expected behavior:

myType.arguments[i] is left unmodified or translated to something equivalent

Actual behavior:

myType.arguments[i] becomes myType.arguments_1[i].

"use strict";
function myFunction(myType) {
    var _loop_1 = function (i) {
        console.log(myType.arguments_1[i]);
        // create closure so that tsc will turn loop body into function
        var x = 5;
        [1, 2, 3].forEach(function (j) {
            console.log(x);
        });
    };
    var arguments_1 = arguments;
    for (var i = 0; i < 10; i++) {
        _loop_1(i);
    }
}
exports.myFunction = myFunction;

ES5 permits keywords to be used as object properties.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Reserved_word_usage

If in aspiring to be a superset of javascript, typescript also wants to allow keywords to be used as object properties, then myType.arguments[i] should stay unchanged or become something equivalent. If not, then typescript should raise an error. Currently no error is raised, and incorrect javascript is generated.