error on for...of statement

[n-a-m-e]

Firstly thanks for writing jslint, secondly I found this new for-of loop that javascript has https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of but js lint throws the error

Expected ';' and instead saw 'of'.

(function(){
    'use strict';
    let arr = [3, 5, 7];
    let i;
    arr.foo = "hello";

    for (i of arr) {
        console.log(i); // logs "3", "5", "7", "hello"
    }
}());

I could always use forEach instead but then I can't break out of the loop

(function () {
    'use strict';
    let arr = [3, 5, 7];
    arr.foo = "hello";
    arr.forEach(function (element, index) {
        console.log(element); // logs "3", "5", "7"
        console.log(index);   // logs "0", "1", "2"
    });
}());

what is your opinion, is the for of loop useful or should I use something else instead. Thanks