I have a JavaScript object as follows:
var a = { Prop1: 'test', Prop2: 'test2' } How would I change the property name of Prop1 to Prop3?
I tried the following code but it didn't work...
for (var p in r){ p.propertyName = 'Prop3'; } 
4 Answers
That isn't directly possible.
You can just write
a.Prop3 = a.Prop1; delete a.Prop1; 
4 Comments
Dmitry Efimenko
the
delete function is usually frowned upon for its performance. Would not it be better to recreate an object?
user276648
@Dmitry: only ask yourself this question if you realize your app is slow because you're using delete. Also I guess creating a new object might be longer if there are lots of properties.
SLaks
@user276648: Plus GC churn.
Cloxure
@Dmitry what are the downsides of using 'delete'?
Another approach would be to use the proposed property rest notation like so:
const {Prop1, ...otherProps} = a; const newObj = {Prop3: Prop1, ...otherProps}; This is supported by Babel's object rest spread transform.
Comments
Adding to the object rest spread solution
const { Prop1: Prop3, ...otherProps } = a; const newObj = { Prop3, ...otherProps }; 
Comments
A simple way to do this is by using if():
for (key in a){ if (key == "Prop1") { key = "Prop3"; } } You can use strict equality === too, making no difference as you will use a string nevertheless
1 Comment
Ricardo
Dear @Lefteris, are you a) joking, or b) something else? And before you get all worked up with this quest of mine to eradicate this kind of answer, here's my usual advice: TRY YOUR OWN CODE BEFORE YOU POST IT!!! It's wildly evident that this will not work, because you're just changing the cycle variable
key's value, not the actual object a's property name. Automagic is not part of the coding game, and assignment — as occurs on the for variable key during cycle — is a one-way thing. Always always always try your code before posting.
var a = { Prop1: 'test', Prop2: 'test2' }isn't JSON data. It's a JavaScript object literal that could be translated into JSON data if you chose to do so.