check.js

function abc(obj, prop) {
    for (let j = 0; j < 1e7; j++) {
        var x = obj[prop];
    }
    return x;
}

function abc2(obj) {
    for (let j = 0; j < 1e7; j++) {
        var x = obj.b;
    }
    return x;
}


var obj = {a: 1, b: 2, c: 3}
abc(obj, 'a');
abc(obj, 'b');
abc(obj, 'c');

console.time('perf');
abc(obj, 'b');
console.timeEnd('perf');

console.time('perf');
abc2(obj);
console.timeEnd('perf');