03 - Annotating _.map

gistfile1.txt

//we create  an object called _
var _ = {
  //the first property is called map it's a method that takes two arguments
  //the first argument is list, the second is a call back function
  map: function(list, cbFn) {
    //this funciton creates a new array
    var newArray = [];
    //it uses a forEach loop to go through list returning the element i'm not sure what index is doing?
    list.forEach(function(elem, index) {
      //im not sure why it's setting the cbFn as a variable here instead
      //of just putting the cbfn into the new Array
      var newElem = cbFn(elem, index);
      //here it pushes the neweEleme variable into the new Array
      newArray.push(newElem);
    });
    //here it returns the new Array
    return newArray;
  }
};
 //the method is invoked passing in the array 1,2,3 and a new function that multiplies the 1,2,3 by 3
 //reading the underscore.js documentationo, i get that it is "transforming" the array passed in, but I'm failing to see how this is helpful right now...
 //it looks like it's an array passin into an array.
 //in my defense i put my thumb up sideways as far as how I felt on this!!
_.map([1, 2, 3], function(num){ return num * 3; });
// => [3, 6, 9]

https://gist.github.com/donoage/0697fbc640bcd7833865b294d73313d8