What is the best way delete elements from java script array by iterating it?

Question

I wrote a piece of code which removes elements from an array while iterating it.

func_name: function (elementsArray) {
  var orig_Array = [10,20,30,40];
  for(var i=0; i < orig_Array.length; i++) {
    if(elementsArray.indexOf(orig_Array[i]) > -1) {
      orig_Array.splice(i, 1);
      i--; 
    }
  }
}

Which is working perfectly fine, But when I sent for review, My reviewer said that manipulating an array while iterating it is a dangerous practice, which in other languages like java leads to concurrentModificationException.

So he suggested me two ways for the above requirement. 1.) Store the elements which I don't want to delete, in a temporary array, and then re-assign the original array with temporary array, here is the code I implemented for this.

func_name: function (elementsArray) {
  var tempArray = [];
  var orig_array = [10,20,30,40,50];
  orig_array.forEach(function (element) {
    if (elementsArray.indexOf(element) > -1) {
      tempArray.push(element);
    }
  });
  orig_array = tempArray;
}

2.) Store the indexes of the elements which I want to delete from the original array, then iterate the indexesArray in reverse order and remove the elements from the original array using splice, here is the code I implemented for the second approach.

func_name: function (elementsArray) {
  var indexesArray = [];
  var orig_array = [10,20,30,40,50];
  orig_array.forEach(function(element, index) {
    if(elementsArray.indexOf(element) > -1){
       indexesArray.push(index);
    }
  });
}

for (var i = indexesArray.length; i >= 0; i--) {
  orig_array.splice(i, 1);
}

Can someone please suggest which is the best way to proceed, and also suggest if there is any other best way to achieve it.

I think your question would be better tailored towards Code Review. If you agree you can close this question and re-ask over there. — JasonWilczak
– JasonWilczak, Commented Jun 12, 2015 at 13:10
I've never seen that error in Javascript, somebody produce it for me. I fail to see how can i do it using forEach — Muhammad Umer
– Muhammad Umer, Commented Jun 12, 2015 at 13:12
This is not java, js has dynamic arrays so this is irrelevant. — Muhammad Umer
– Muhammad Umer, Commented Jun 12, 2015 at 13:15
You will be fine to iterate over the array backwards. So start at the array length and go down to zero. You would get the error you're talking about in .net too so you have to go backwards. This applies most languages that I can think of. — Darren Wainwright
– Darren Wainwright, Commented Jun 12, 2015 at 14:12

hindmost · Accepted Answer · 2015-06-12 13:15:35Z

3

You can use Array's filter method instead of iterating:

func_name: function (elementsArray) {
  var orig_Array = [10,20,30,40];
  orig_Array = orig_Array.filter(function(el) {
    return elementsArray.indexOf(el) < 0;
  });
}

answered Jun 12, 2015 at 13:15

hindmost

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Comments

Community · Accepted Answer · 2017-05-23 11:58:35Z

This is how I'd usually always delete an item from an array. It's as simple as this, you can then add a loop.

var testArray = ["12","13","14","15"];
var indexItem = testArray.indexOf("14");
if (indexItem >= 0) {
  arr.splice( indexItem, 1 );
  console.log(testArray);
}

Loop

Array.prototype.deleteItem = function(val) {
    var indexItem = this.indexOf(val); 
    if (indexItem >= 0) this.splice(indexItem, 1);
    return this;
}; 

var testArray = ["12","13","14","15"];
var newTestArray = testArray.deleteItem("14");

console.log(newTestArray);

Also as hindmost said you can use Array's filter method instead of iterating

func_name: function (elementsArray) {
  var orig_Array = [10,20,30,40];
  orig_Array = orig_Array.filter(function(el) {
     return elementsArray.indexOf(el) < 0;
  });
}

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