x+=y+=z in Javascript

Question

I know in javascript

x = y = z means x = z and y = z

x+=z means x=x+z;

So if I want x=x+z and y=y+z, I tried x+=y+=z not working

anyone have a better idea to write short code instead x+=z;y+=z

EDIT

First thanks for everyone involved in my question. Here I wanna explain something why I have this question in first place.

I tried to write some code like x+='some html code', and I need to y+='the same html code'. So naturally I do not want to create another var z='the html code first then do x+=z and y+=z

Hope my explain make sense. Anyway, I am going to close this question now. Thanks again.

Answer 1

Assuming addition, and not concatenation, this works:

x -= y - (y += z);

but seriously, don't use it !

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For those that want to figure out how, the sequence of evaluation (where I use n to show the current intermediate result) is approximately:

n = y1 = y0 + z  //    n = y = (y + z)
n = y0 - y1      // -> n == -z  [uses the original value of y]
x -= n           // -> x += z

Answer 2

Just use this:

x+=z;y+=z

Honestly, anything else is just going to cause somebody else maintaining your code to stop and scratch their head for a couple of minutes. This code isn't shockingly long either...