var vs let

var abc = [ 'a', 'b', 'c' ];
var cbs1 = [], cbs2 = [];

for (var i = 0; i !== abc.length; i++) {
        var symbol = abc[i];
        cbs1.push(() => symbol);
}

for (var i = 0; i !== abc.length; i++) {
        let symbol = abc[i];
        cbs2.push(() => symbol);
}



console.log(cbs1.map((f) => f()).reduce((s, sym) => s+sym)); // "ccc"
console.log(cbs2.map((f) => f()).reduce((s, sym) => s+sym)); // "abc"