Javascript function return

Question

function abc(a) {
return (function(y) {
return y + 1;
})
(++a) + a
}
document.write(abc(2))

The output is 7 but I don't understand two things below:

1. 'return' part comes first even though it should be placed in the end; because it stops func execution. When I put '(++a) + a' in the beginning and 'return' part in the end of the func block, however, it doesn't work properly.

2. Based on the output, it seems that '(++a) + a' is assigned to y parameter. But why?

Please someone help me grasp the whole flow of this code. Thanks in advance.

Answer 1

This questions involves two JavaScript concepts: IIFE and ASI.

Firstly, function(y){return y + 1;} itself is a function, when you wrap them with parenthesis, you are going to add another parenthesis to execute it.

(function(y){return y +1;})(4) will be the same as
function addOne(y){
return y+1;
}
addOne(4);

that's the immediately-invoked function expression part.

2. for ending a line at }), as explained above, because it is IIFE, the compiler do not perform automatic semicolon insertion here; instead of ASI, it append the next line to the current line.

3. So the execution is
return addOne(++a) + a.

So noted that you are wrong in that the + a part also put into as y, actually only the (++a) because it is in parenthesis.

4. the variables changes
a is 2,
++a is executed, a becomes 3,
y is 3,
4 is returned,
a is 3 now, so (4) + 3,
so result is 7.

5. To Rai, Kuba's explanation is wrong.

Answer 2

Gordon Masterfully and thoroughly answered.

I can't find one thing wrong with your various points.

I only wanted to add a link to a fantastic article I found a few years ago regarding ASI in Javascript.

https://2ality.com/2011/05/semicolon-insertion.html

Answer 3

The function in parentasis is an anonmymous function called with argument (++a). The return value of this function is then added to a.
You can do a separate function for the nested function and name it for exemple "myFunction". The final result would look more clear :
function abc(a) {
return myFunction(++a) + a;
}

Answer 4

//In short it working like this

//example code like above
((name)=>{
this.user = name
console.log(user+'doe')
})('john')

//Please see this thread similar already answered
https://www.sololearn.com/Discuss/1756451/function-abc-a-return-function-y-return-y-1-a-a-alert-abc-2
https://www.sololearn.com/Discuss/482453/?ref=app

Answer 5

Thanks, Gordon. You're the best.

Answer 6

what have you written...?!😱