Have seen many usage in this format:
(0, function(a, b){console.log(a + b)})(3, 4)
What is 0 for?
Asked
Active
Viewed 73 times
1
-
1`function(a, b){console.log(a + b)}(3,4)` is not a valid syntax. That's why the author of that code used comma expression to call it. Author would have written the same code like, `(function(a, b){console.log(a + b)})(3,4)` – Rajaprabhu Aravindasamy Sep 19 '16 at 06:58
-
@RajaprabhuAravindasamy but `(function(a, b){console.log(a + b)})(3,4)` is valid – Hom Sep 19 '16 at 07:04
-
It's just another IIFE syntax. I also don't understand why the author chose to use a comma – evolutionxbox Sep 19 '16 at 07:07
2 Answers
-1
That 0 is ignored.
That comma is the comma operator:
The comma operator evaluates each of its operands (from left to right) and returns the value of the last operand.
Basically that 0 is evaluated as 0 then that function expression is evaluated and since the function is the last thing evaluated in the comma list a function reference to it is returned. It is that returned function that is called.
In the code in your question, the 0 is therefore completely useless.
However, it could be that the author intended this instead:
0,function(a, b){console.log(a + b)}(3, 4);
Which saves typing two characters ( and ) but then it takes two characters anyway so it's not very useful.
slebetman
- 109,858
- 19
- 140
- 171
-1
It serves the same purpose as a parenthesis or a bang prefix.
0 is an expression that has no effect. The comma operator puts the right hand side into experssion context.
This means that function is then treated as the start of a function expression (which can be an IIFE) instead of a function declaration (which would throw an error if you tried to treat it as an IIFE, which this code does by following it with (3, 4)).
