iterators.js

var obj = { foo: "bar", wut: "what" };
var arr = [1,2,3,4,5];

obj[Symbol.iterator] = function() {
    let keys = Object.keys(this);
    let nextIndex = 0;
    return {
        next() {
            return nextIndex < keys.length ?
                { value: keys[nextIndex++], done: false } :
                { value: void 0, done: true };
        }
    };
};

arr[Symbol.iterator] = function() {
    var nextIndex = 0;
    return {
        next() {
            return nextIndex < this.length ?
                { value: this[nextIndex++], done: false } :
                { value: void 0, done: true };
        }
    };
};

console.log([...obj]);

for(let o of obj) {
    console.log('=', o);
}

console.log([...arr]);
for(let x of arr) {
    console.log('-', x);
}