JS: Comparing Arrays and adding new items or removing items no longer in array

Question

When I query my DB for items i generate an array say a list like

 ArrayOne =  [Apple, Banana, Orange, Banana] 
//yes, an item can be there twice or more

then I duplicate it in a ArrayOne_Copy = ArrayOne

ok, then after an interval of 5 minutes I check again the DB and generate and replace the array ArrayOne say now is like

 ArrayOne =  [Apple, Peach, Banana, Pineapple, Banana, Melon] 

at this point I want to compare the ArrayOne_Copy with the newly generated ArrayOne and rebuild the list from the new list but without clearing the list and generating a new output, but i want to only add the new items or remove the one no longer in the list

if I can "speak" code I would tell the script to:

Don't touch `Apple` because has not changed
Push 'Peach" between `Apple` and `Banana`
Push `Pineapple` between `Banana` and `Banana`
Remove `Orange`
Add `Melon`

so. I'm kinda lost, and maybe the solution is very simple. Can you suggest the best practice?

Answer 1

You're not duplicating it, you're referencing it.

You will need to make a hard copy of the array which can be done using slice() .

var ArrayOne_Copy = ArrayOne.slice(0);

---

For example:

var ArrayOne = ['Apple', 'Banana', 'Orange', 'Banana'];

var ArrayOne_Copy = ArrayOne.slice(0);

ArrayOne.push('Melon');

console.log(ArrayOne);
console.log(ArrayOne_Copy);

http://jsfiddle.net/y7czyn3h/

http://davidwalsh.name/javascript-clone-array

Answer 2

You can use this kind of function:

Array.prototype.complete = function( arr ){
  var result = new Array();
  for( var a in arr )
    result[ a ] = this[ a ] ? this[ a ] : arr[ a ];
  return result;
}

Like this :

ArrayFull = ArrayOne_Copy.complete( ArrayOne );

Then ArrayFull will be the array modified with .