Homework 3 underscore map.js description

gistfile1.js

// This is the creation of a variable called "_" which is a method
// Stephen: Not a method. variable '_' is an object.
var _ = {
  // on this line the first key value is function (so a function within the variable method).
  // This function will take to params: list and cbFn
  // Stephen: this map() function is a property of '_' object that takes an array and a function reference as their params.
  map: function(list, cbFn) {
    // within the method's function, there is a new local variable, newArray, which is an empty array
    // Stephen: We establish 'newArray', which is an empty array to store the result from forEach() below.
    var newArray = [];
    // on this line we're showing each element/item created by the parameter "list"
    // Stephen: We are invoking forEach() array method on our list parameter.
    list.forEach(function(elem, index) {   
       // creating a new variable using the CbFn parameter and the elements and index generated by the list function
      // Stephen: We are invoking our anonoymous function cbFn() to convert each item from array 'list' and,
      // storing the result to the variable 'newElem'.
      var newElem = cbFn(elem, index); 
      // the newArray variable is using the push vanilla JS method to create an array using the dynamic variables created by newElem
      // Stpehen: we are not creating a new array each time but pushing each converted elem to newArray we established above.
      newArray.push(newElem); 
    });
    
    // Stephen: after iterating and converting each item in 'list', return back the newArray to original function invocation line.
    return newArray;
  }
};
// this shows the result of the _ variable .map takes 3 objects within an array, converts them using a number parameter, 
// multiplies them by three and generates a new array based on the new results.
_.map([1, 2, 3], function(num){ return num * 3; });