/*
 * Loops
 *
 * loops are blocks of code that is repeated
 * they go until a certain condition is met
 *
 */

/* for loop
 *
 * for(variable; condition; increment) {
 *    // code to be repeated
 * }
 *
 */

for(let i = 0; i < 3; i++) {
  console.log(i);
} // -> 0..1..2

/* first it sets the variable (let i = 0)

 * then it checks the condition (i < 3) 0 < 3
 * it is, so it will execute the code block (console.log(i))
 * after the code block was executed it increments i (i++) i = 1
 *
 * then it checks the condition (i < 3) 1 < 3
 * it is, so it will execute the code block (console.log(i))
 * after the code block was executed it increments i (i++) i = 2
 *
 * then it checks the condition (i < 3) 2 < 3
 * it is, so it will execute the code block (console.log(i))
 * after the code block was executed it increments i (i++) i = 3
 *
 * then it checks the condition (i < 3) 3 < 3

 * it is not true, so the loop ends
 */


// we can quickly loop over the elements of an array with a loop like so:
const arr = [7, 'hi', {}, [], 33];
for(let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
}

// and in reverse:
for(let i = arr.length-1; i >= 0; i--) {
  console.log(arr[i]);
}


/* for in loop
 * designed for looping for objects
 *
 * for(variable in object) {
 *    console.log(variable);         // logs the key
 *    console.log(object[variable]); // logs the value
 * }
 */

const person = {
  name: 'cain',
  id: 234,
  isHuman: true
};

for(let key in person) {
  console.log(key + ': ' + person[key]);
} // -> name: cain..id: 234..isHuman: true


/* while loop
 *
 * a while loop runs until the condition is met
 *
 * while(condition) {
 *   // code to be executed
 * }
 */
let x = 8;
while(x < 12) {
  console.log(x);
  x++;
} // -> 8..9..10..11