JavaScript Access to object and set it null throw element of array access via null object reference,access vba is null object

Very simple example:

var a = { id: 5 };
var b = { id: 6 };
var c = { id: 7 };
var arr = [a, b, c];

Now i have a function:

function remove(startIndex) {
  // set objects to null from startIndex in array
}

If i try this:

arr[0] = null;

then i have:

arr[0] == null // true
a == null // false (i need true)

So, my question, how could i access to object throw any collection (array or object) and change it?

I don't want to write something like this:

function remove(startIndex) {
  if(startIndex == 0) { 
    a = null;
    b = null;
    c = null;
  }
  if(startIndex == 1) {
    b = null;
    c = null;
  }
  if(startIndex == 2) {
    c = null;
  }
}

much easier to write like this (but it doesn't work):

function remove(startIndex) {
  for(var i = startIndex; i<arr.length; i++) arr[i] = null;
}
Answer:1

I don't know exactly what you're aiming with this code you're writing, but here's how Javascript works:

Every time you instantiate a variable with a value, say an object like { id: 10 }. That object is stored in memory and a reference is returned back to your variable, say you name it a.

Now, if you say var b = a;, the same reference is now passed on to variable b. Now Javascript runtime knows you have two variables referencing the object { id: 10 }.

You now no longer want to keep the variable b, so you write b = null;. You think the object is deleted, but the Javascript runtime knows the object { id: 10 } has one reference -- i.e. the variable a -- referencing it. So it won't remove { id: 10 } from memory.

However, if you also write a = null;, then there are Zero references, and the Javascript runtime's Garbage Collector will eventually get to removing the object from memory.

All this was to get you to understand that without further housekeeping, you will not be able to achieve what you're hoping to do.

If you really want a, b, c to be null, you will have to write some code that explicitly sets their value to null too. Like a = arr[0]; b = arr[1]; c = arr[2]; whenever the array is changed. You can eval the statements and do some string templating to not write the variables by hand etc., and make a loop out of that, but that's not worth it if you only have three variables.

Hope this helps.

Answer:2

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