Write a function “groupBy(array, callback)”

Question

I have a JavaScript task where I have to implement a function \"groupBy\", which, when given an array of objects and a function, returns an object w

Answer 1

Heres a link to the code: http://rextester.com/KROB29161

function groupBy(list, callback) {
  // Declare a empty object
  var obj = {};

  // We then loop through the array
  list.forEach(function(item) {
    // We define the key of the object by calling the 
    // callback with the current item
    var key = callback(item);

    // If the field exists, add this item to it
    if (obj[key]) {
      obj[key] = obj[key].concat(item);
    } else {

      // If the field does not exist, create it and this value
      // as an array 
      obj[key] = [item];
    }
  });
  return obj;
}