LoopingLooping studies// source https://jsbin.com/fuqawu

jsbin.fuqawu.js

// -----Loops----- //

/* For loops are great tools for iterating over individual elements within an array
to work with them. A for loop has three sections within its proceeding parentheses: an 
initialization, conditional statement, and a final expression. The initialization phase
usually declares a variable. The conditional statement phase tells the loop when to stop,
and the final expression performs an action at the end, usually incrementing or 
decrementing a counter: */

"use strict";

var arr = ["What is love?", "I love you", "I hate you", 24, "Baby, don't hurt me"];

for (var i = 0; i < arr.length; i++) {
  if (i === 0 || i === 4) {
    console.log(arr[i]);
  }
}

/* It is possible to loop through the array in more than one direction: */

for (var i = arr.length; i > 0; i--) {
  if (i === 2) {
    console.log(arr[i]);
  }
}

/* a while loop is similar to a for loop, except a while loop only contains a conditional
statement within its parentheses. It will require a counter of some sort to tell the loop
when to stop. This counter is easy to forget but VERY important; executing a while loop without
it will cause an infinite loop and possibly crash the program. */

var n = 0;

while (n < 3) {
  console.log("Beatlejuice");
  n += 1; // super important to remember
}

/* A for in loop does for objects what the for loop does for an array--it iterates over the
object's enumerable properties and performs an action at every stop. */

var obj = {
  a: 1,
  b: 2,
  c: 3
};

for (var key in obj) {
  console.log(key + ": " + obj[key]);
}

/* Since objects are innately unsorted and looping through in a particular order can't be 
guaranteed,to get closer to looping in the order you wish, some external arranging must first
take place. For example, using a regular for in loop may iterate through the key/values in the 
order they were assigned. To loop backwards, you could extract the keys and place them into an 
array, reverse the order of the array, and then use a for loop to iterate through the array and 
return a new object: */

function reverseObj(object) {

  var newObj = {};
  var arr = Object.keys(object);

  arr.reverse(); // could also skip this line and iterate backwards in the for loop instead

  for (var i = 0; i < arr.length; i++) {
    newObj[arr[i]] = obj[arr[i]];
    //     console.log(newObj); Uncomment me and you will see it insert the key/values in reverse
  }
  return newObj;
}

reverseObj(obj);

/* Depending on which browser or program runs this code, it may still log it in the console
in alphabetical order, but logging within the for loop displays the correct results. */