custom-iterator.js

var obj = {
	values: [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34],
	start: 4,
	end: 13,
	[Symbol.iterator]() {
		var idx = this.start;
		var end = this.end;

		var it = {
			next: () => {
				if (idx <= end) {
					var v = this.values[idx];
                    idx += 1;
                    return {
                        value: v,
                        done: false,
                    };
				} else {
					return {
						value: undefined,
						done: true,
					};
				}
			}
		};
		return it;	
	},
};

var myCustomArr = [ ...obj ];
console.log(myCustomArr);