pass an expression to a javascript function

Question

I have the following code from a javascript book and the callback seems to be passed an expression as an argument. Is that the case or am I seeing this wrong? I didnt know, even though it works, that that was possible.

function multiplybytwo(a,b,c,callback)  {
  var i, ar =[];
  for(i=0;i<3;i++)  
  {
    ar[i] = callback(arguments[i]*2);  
  }
  return ar;  
}  

function addone(a)  {
  return a+1;  
} 

myarr =multiplybytwo(1,2,3,addone);

No, you're not seeing this wrong, you can pass functions to other functions as arguments. (I suggest you grab a lambda calculus book if this seems weird.) — user529758
– user529758, Commented Dec 17, 2012 at 0:12
Calling a function and passing an expression as an argument is pretty standard in every language that I'd care to use - it's not just a JS thing. The expression is evaluated and the resulting value is passed to the function. Note that even something simple like someFunc(1) is passing an expression to a function, it's just that the expression is a simple number, 1 - but you can put pretty much any expression, including things that call other functions, e.g., someFunc(someOtherFunc(x*2) / 7 + (aThirdFunc() ? 1 : -1)) — nnnnnn
– nnnnnn, Commented Dec 17, 2012 at 0:13

Majid Laissi · Accepted Answer · 2012-12-17 00:08:32Z

1

callback(arguments[i]*2);

is equivalent to

var a = arguments[i]*2;
callback(a);

Same as callback(1+2); to callback(3);

answered Dec 17, 2012 at 0:08

Majid Laissi

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timc · Accepted Answer · 2012-12-17 00:05:53Z

0

The callback is passed the result of that expression.

answered Dec 17, 2012 at 0:05

timc

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Comments

Bruno · Accepted Answer · 2012-12-17 00:15:14Z

0

Arguments are evaluated before they are passed to functions.

function foo( a ) {
    alert( a );
}

function bar( ) {
    return 1;
}

foo( bar( ) );

The above (demo) will display 1.

answered Dec 17, 2012 at 0:15

Bruno

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