CODEWITHSUNDEEP
javascriptternary-operator
newguy
newguy

Reputation: 5986

Need clarification using 0 with ternary operator

I am reading source codes written in a game. Some lines are written as follows:

0 ? player.y > global.screenHeight/2 : global.screenHeight/2 - player.y

Assume that player is a sprite with position and global is just an import from other files which contains some properties. What does the above code do? I thought the ternary operator will be something like this:

c ? a : b

where a and b are of the same type and c is the condition.

But the game demo runs smoothly so the above code should be fine. I just don’t get the meaning of the code.

The code is extracted from here:
https://github.com/huytd/agar.io-clone/blob/master/src/client/js/app.js

Upvotes: 1

Views: 115

Answers (3)

Moishe Lipsker
Moishe Lipsker

Reputation: 3032

In the above ternary statement 0 is the condition.

Because Javascript treats 0 as falsy, the statement is evaluated as if written as:

false ? player.y > global.screenHeight/2 : global.screenHeight/2 - player.y

Therefore, global.screenHeight/2 - player.y will be returned.

It is possible the author put the ternary there to act as an on/off switch. By replacing the 0 with a 1, the ternary statement would return player.y > global.screenHeight/2 instead.

Upvotes: 1

Venkat
Venkat

Reputation: 2579

0 ? player.y > global.screenHeight/2 : global.screenHeight/2 - player.y

Here 0 is false , So the global.screenHeight/2 - player.y will be always executed

Upvotes: 0

VortixDev
VortixDev

Reputation: 1013

c ? a : b

a and b can evaluate to values of any type, and c will evaluate to true or false.

0 will evaluate to false, "b" will run: global.screenHeight/2 - player.y This will happen regardless of anything else - the first expression will never run.

If I had to guess why that's in there, I'd say it may be a placeholder for a planned feature or improvement (however I obviously can't know for sure).

Upvotes: 0

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