set value of object stored in variable to null

Question

So I just discovered today that doing this:

a = { b: { c: 1, d: 2 }, d: {} }
sub = a.b
// sub is { c: 1, d: 2 }

sub is now actually the object stored in a, not a clone.

Now if I do this:

sub.c = "x"
// a is now: { b: { c: 'x', d: 2 }, d: {} } // nice

The same thing applies to arrays.

So I have this array:

arr = [{a: 1, b: 2}, {c: 3, d: 4}]
sub = arr[1]

I'd like to remove sub from array so that arr becomes: [{a: 1, b: 2}] but if I do sub = null I simply assign a new value to sub. Same thing for delete.

delete sub // will unset the sub variable, not the object that it references.

So the question is: how do I remove {c: 3, d: 4} from the array by using sub

Even though it works, I can't use delete arr[1] because I don't know the index. I'm storing the object using the min function of lodash

You can't. arr[1] and sub are both references to the same object, but sub is not pointer to the array itself. — Barmar
– Barmar, Commented Oct 9, 2014 at 13:51
Please note that there is a big difference between sub.c = "x" and sub = null. In the first case you are reading the value of sub and mutate the object, in the second you are writing a new value to sub. — Felix Kling
– Felix Kling, Commented Oct 9, 2014 at 14:17

dfsq · Accepted Answer · 2014-10-09 13:57:35Z

3

To delete element from array, be it primitive value or object, you still use splice. To find element index you would use indexOf. It possible because:

indexOf compares searchElement to elements of the Array using strict equality (the same method used by the ===, or triple-equals, operator).

So combined together

arr.splice(arr.indexOf(sub), 1);

Take a look at this demo:

var arr = [{a: 1, b: 2}, {c: 3, d: 4}]
var sub = arr[1];

alert('Before: ' + JSON.stringify(arr));

arr.splice(arr.indexOf(sub), 1);

alert('After: ' + JSON.stringify(arr));

edited Oct 9, 2014 at 13:57

answered Oct 9, 2014 at 13:52

dfsq

193k26 gold badges244 silver badges261 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Quentin · Accepted Answer · 2014-10-09 13:57:16Z

2

So the question is: how do I remove {c: 3, d: 4} from the array by using sub

There is no way to do that directly.

Relationships in JavaScript are one-way.

sub is a reference to an object. arr[1] is a reference to the same object.

There is no direct way to get from the object to sub or to arr[1].

Since you know arr contains a reference to the object, you can search for a copy of that reference using indexOf.

var index = arr.indexOf(sub);

You can then use it to remove the element from the array.

arr.splice(index, 1);

answered Oct 9, 2014 at 13:57

Quentin

949k136 gold badges1.3k silver badges1.4k bronze badges

Collectives™ on Stack Overflow

set value of object stored in variable to null

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related