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Function passed to function

Posted on 2011-05-10
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Last Modified: 2012-05-11
Hi All,

Can someone explain to me how the attached code works?
I understand the 3 and 4 are passed as the x and y parameters and the function is passed as the z parameter.. But i don understand  what parameters are being passed to: function(x,y) { return x * y}??
Also, what is happening in the following line:
alert(z(x,y));


Thanks



function funcObject(x,y,z) {
   alert(z(x,y));
}

function testFunction() {

// third parameter is function
funcObject(3,4,function(x,y) { return x * y})
}

testFunction();

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Question by:oggiemc
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6 Comments
 
LVL 9

Accepted Solution

by:
Roman Gherman earned 1500 total points
ID: 35731313
Hi,

Javascript allows you to pass any object as a parameter to a function.

A function is basically an object in javascript, this is why in the example you provided you have a function as the third parameter.

"alert(z(x,y));" - will call the function passed in parameter z with the two parameters: x and y.

this will show an dialog containing the TEXT: 12.  
x*y = 12;
0
 
LVL 13

Assisted Solution

by:dsmile
dsmile earned 500 total points
ID: 35731332
No params are passed to function(x,y) { return x * y}
It's function definition that is passed to funcObject()

12 will be the result of alert
0
 

Author Comment

by:oggiemc
ID: 35731540
Thanks for reply guys..Unfortunately i still dont see where the actual multiplication of x * y is happening??

roma
\\ "alert(z(x,y));" - will call the function passed in parameter z with the two parameters: x and y.

so what you are saying is that above line is equivalent to:
alert(function(x,y) { return x * y}(x,y));   // i.e z = function(x,y) { return x * y}?

it all looks a bit confusing to me, and im not really sure what is the point of this technique?? Perhaps someone can enlighten me / explain in a bit more detail?
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LVL 9

Assisted Solution

by:Roman Gherman
Roman Gherman earned 1500 total points
ID: 35731629
yes, that is correct.

that syntax is called anonymous function.
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Author Comment

by:oggiemc
ID: 35732781
alert(z(x,y));

So all the above line means is:

The z function i.e function(x,y) { return x * y} is called, and the x,y parameters are passed in to it?? I understand it is called an anonymous function, however i do not understand why such functions are used? What is the advantage over declarative functions?

thanks
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LVL 9

Assisted Solution

by:Roman Gherman
Roman Gherman earned 1500 total points
ID: 35735231
yes the x,y parameters are passed in to it

take a look at this page with explanations: http://helephant.com/2008/08/23/javascript-anonymous-functions/
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