Adding a custom iterator to a javascript class

With ES2015 its simple:

function Range(start, end) {
    var ret = {};
    ret[Symbol.iterator] = function *() {
        while (start < end) 
            yield start++;
    }
    return ret;
}

Though you have to use:

for (var x of Range(1, 10))

With ES2015 it can be even more simple

const Range = (start, end) => ({
  *[Symbol.iterator]() {
    while (start < end) 
        yield start++;
  }
})

for (var x of Range(1, 10)) {
  console.log(x)
}