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Thread: Beginner's question

  1. #1
    Join Date
    Mar 2013
    Posts
    4

    Beginner's question

    Hi,

    In the following example :

    function makeAddFunction(amount) {
    function add(number) {
    return number + amount;
    }
    return add;
    }

    var addTwo = makeAddFunction(2);
    var addFive = makeAddFunction(5);
    show(addTwo(1) + addFive(1));

    The answer is 9. I understand very well that makeAddFunction(2)'s value is 2 and is used to replace the term (amount) in the first line and the same applies to makeAddFunction(5) for 5 as a value.

    What I cannot explain though is how the program uses 1 as a value for add(number).There is no link at first glance between function add(number) and addTwo(1) or addFive(1). Can anyone show me how the program sets 1 as a value for those last two variables?

    Thank you!

    Laurent

  2. #2
    Join Date
    Oct 2010
    Location
    Versailles, France
    Posts
    1,276
    What is the function add(number) ?

  3. #3
    Join Date
    Mar 2013
    Posts
    4
    You see, this is where I get confused. The (1) in addTwo(1) and addFive(1) are assigned to number in add(number) but I don't understand how this variable is assigned. Maybe it's the syntax that I don't understand. Can anyone help me on this?

    Thanks again,

    Laurent

  4. #4
    Join Date
    Oct 2010
    Location
    Versailles, France
    Posts
    1,276
    Sorry I have not seen ! Two remarks :
    1/ - You have build a closure,
    2/- number, which is an argument of the function, has the value 1. It's the same thing with foobar then one would expect undefined ???
    Last edited by 007Julien; 03-26-2013 at 10:02 AM.

  5. #5
    Join Date
    Dec 2012
    Location
    NSW Australia
    Posts
    73
    As has been pointed out it is a closure that makes use of an inner function.

    the variables have a memory to the original numbers to use when you call it with the 1

    the two keyword to use in searching will be
    closure and inner function

    just to start you off

    https://developer.mozilla.org/en-US/...nner_functions

  6. #6
    Join Date
    Mar 2013
    Posts
    4
    Thank you guys for your answers. This stuff is new to me, I will take some time to read further in order to understand the concepts. I get the closure part.

    What I still don't understand is how the program sets 1 a the variable for number. As far as I can understand, nothing states in the program the value of number. Actually, something does but I can't figure out what it is.

    Thanks again,


    Laurent

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