Test your recursive knowledge

[agibsonsw]

Hello. (JavaScript)

I have a function (similar to the following) that I would like to accept either a number or an array of numbers as an argument:

Code: Select all

function DoubleThem(num) {
    while (num.length) DoubleThem(num.pop());
    if ( typeof num == 'undefined' || isNaN(num) ) return;
    window.alert(num * 2);
}

But it ends up trying to double an undefined, or non-existent, value/object.

Andy.

[Jezza]

Andrew I haven't tested this but have you tried:

Code: Select all

function DoubleThem(num) 
{
    while (num.length) DoubleThem(num.pop());
    {
    if ( typeof num == 'undefined' || isNaN(num) ) return false;
    }
else
   {
    window.alert(num * 2);
   }
}

[agibsonsw]

Thanks for getting back to me.

I tried something similar with 'undefined' but it didn't work. I think the sticking point is an empty array, which is not undefined.
The following works perfectly:

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while ( col.length ) AddSortByNumber(tbl,col.pop());
if ((col instanceof Array) || isNaN(col)) return;
//this is the actual name of my procedure

I like this method - it's neater than checking for an array or number and then looping through the array. There is an overhead with recursion
but this procedure works with table columns and there will never be a huge number of them.

Thanks again, Andy.

(P.S. it's nice to have an example of recursion which isn't a Edited: Fibonacci series )