Storing value in two variables and changing one affects both variables in Javascript [duplicate]

Question

I have an object "a" and would like to duplicate it to "b" When I delete an element in "a" why is "b" also being affected?

var a  = {'apple':1,'orange':2,'grapes':3}
var b = a 

console.log(a,b)
delete b.apple
console.log(a,b)

Now a and b are the same. I only want the element in b to be deleted. How can I do this

This is a dup of many other answers. I will go find a dup to mark it as such. — jfriend00
– jfriend00, Commented Nov 1, 2015 at 8:51
The reason is that a and b are both references to the same object. You need to clone the object to get what you need. See stackoverflow.com/q/122102/2170192. — Alex Shesterov
– Alex Shesterov, Commented Nov 1, 2015 at 8:52
Note that the linked question explains the mechanism of passing the value to a function. Not the values themselves which is what this question is asking. — slebetman
– slebetman, Commented Nov 1, 2015 at 9:10
@slebetman - I could literally find twenty dups that explain this. Here's another one: stackoverflow.com/a/11837596/816620 and stackoverflow.com/questions/7576884/… and stackoverflow.com/questions/30427395/object-or-objectification/… and stackoverflow.com/questions/13595359/… — jfriend00
– jfriend00, Commented Nov 1, 2015 at 9:12

slebetman · Accepted Answer · 2015-11-02 00:30:47Z

2

Objects and arrays in javascript are references. So when you do:

var b = a;

You're making another pointer to object a. You're not copying a.

If you want to make a copy of an object you can use Object.create:

var b = Object.create(a);

edited Nov 2, 2015 at 0:30

answered Nov 1, 2015 at 8:53

slebetman

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8 Comments

jfriend00 Over a year ago

Seriously, you don't think there are at least 50 dups of this question?

slebetman Over a year ago

@jfriend00: Sometimes it's quicker to just answer than find a good dupe. If I have time I'll find a dup

slebetman Over a year ago

@jfriend00: I know a good answer for function arguments but I don't know of one for just variables.

slebetman Over a year ago

@jfriend00: The answer pointed to by Alex above is a good example of not a good general purpose answer because it's jQuery specific. Even the non-jQuery answers to that question don't explain the WHY, which is what this question is asking.

slebetman Over a year ago

@jfriend00: The answer you duped is another good example of not a good answer for this question. It's a different (but related) question.

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