Parameters of a function variable

Question

After distilling the answers to How are parameters handled when passing functions in Javascript? I ended up with one question I need to clarify.

In the sample below:

function plus2(x) { return x+2; }

var Q = function(y) { return plus2(y); }

alert(Q(10));

Why does the invocation of Q with an argument of 10 result in y getting the value 10?

Would you question y being 10 with: `var Q = function(y) { alert(y); } Q(10);`? — Adrian Lynch, Sep 19 '15 at 16:57
@AdrianLynch Yes I still would, because of my usual understanding of the meaning of the = sign and my poor understanding of functions as first class objects. I replaced the anonymous function with a named function and it became clearer. — Old Geezer, Sep 19 '15 at 17:05

score 0 · Answer 1 · answered Sep 19 '15 at 17:00

function plus2(x) { return x+2; }

var Q = function(y) { return plus2(y); }

alert(Q(10));

Will alert 12. yis 10 as it is the value 10 which is passd as an argument and then assigned to the function parameter y. Equivalent

var y = 10; // call of Q

var x = y; call of plus2 in Q
x = x + 2;

y = x; // return of plus2

alert y; // return of Q

Old Geezer · Accepted Answer · 2015-09-20T01:58:06.150

-2

Replacing the anonymous function with a named function gave me a little bit more clarity:

function plus2(x) { return x+2; }
function dummy(y) { return plus2(y); }

var Q = dummy;

alert(Q(10));

Q then becomes a sort of alias for dummy.

edited Sep 20 '15 at 01:58

answered Sep 19 '15 at 17:00

Old Geezer

2 Answers2