rewriting _.each function in Javascript not returning

Question

rewriting _.each function in Javascript not returning

Im trying to sharpen my skills in JS and rewriting the underscore.js utility functions. I'm stuck on the first one: each. This is what I have so far but when I run it in node, nothing is returned from iterator() being passed to each()? Please help

//_.each(list, iteratee, [context]); iteratee(element,index,list);

var arr = [1,2,3,4];

var each = function(list, iteratee) {
    for (var i = 0; i < list.length; i++) {
        iteratee(list[i], i, list);
    }
}

var iterator = function(element, i, list){
    return element * 2;
}

each(arr,iterator);

What am I doing wrong and what rewriting these functions in the future, what is the best way to do it? Thanks.

javascript
node.js
callback
underscore.js

Answer 1

For your each function to return something you actually need to return something:

var arr = [1,2,3,4];

var each = function(list, iteratee) {
    for (var i = 0; i < list.length; i++) {
        // Write return value back to array
        list[i] = iteratee(list[i], i, list);
    }
    // return array
    return list;
}

var iterator = function(element, i, list){
    return element * 2;
}

each(arr,iterator);

This would return the array, what underscore and other popular libraries are doing is returning a wrapped set to enable chaining(_.each().map().bla()). All these libraries(underscore, lodash) are open source, so i recommend to actually look at the source to understand how they operate.