---

• JavaScript codes to detect if a substring is exists in a string.

var str = "hello world";
var substr = "world";
// This codes will return `true` is `substr` is in `str`.
console.log(str.indexOf(substr) > -1);

• JavaScript to detect multiple indexes in an array (each for the same element).

// Function to return multiple indexes in an array for found element.
function indexesOf (_array, _element) {
  var indexes = [];
  for (var i = 0; i < _array.length; i ++) {
    if (_array[i] == _element) indexes.push(i);
  }

  return indexes;
}

• Multiple replace() in JavaScript.

str = "asdasd".split(replaceThisString).join(withThisString);

• How to make sure that a JavaScript array is unique.

arr = Array.from(new Set(arr));

• This is the reference from StackOverflow to make unique array, https://stackoverflow.com/questions/1960473/unique-values-in-an-array.
• Here is an example codes on how to convert string into array of characters.

"asdasd".split("");