Trying to understand this function in Javascript

resetreset · 12-09-2010, 02:09 PM

Hi,
In my book, this is an example of a recursive algorithm:

var reverseArray = function(x,indx,str) {
return indx == 0 ? str : reverseArray(x,--indx,(str+= " " + x[indx])) ;;
}

var arr = new Array('apple','orange','peach','lime');
var str = reverseArray(arr,arr.length,"");
alert(str) ;

I'm trying to understand it, I'm stuck at the (str+= " " + x[indx])) part - that part of the function definition expects an ARGUMENT, am I right? What's being passed to it is a bit of PROGRAM, the str+= stuff. So - how is it working?

tsg · 12-09-2010, 02:37 PM

The str+= " " + x[indx] part is a bit of shorthand. What it is doing is appending " " + x[indx] to str and then passing str as an argument to reverseArray(). It is identical to writing:

Code:

--indx;
str += " " + x[indx];
reverseArray(x,indx,str);

resetreset · 12-09-2010, 02:45 PM

But how is this happening? How will I know what forms a part of an argument?

tsg · 12-09-2010, 02:55 PM

The commas between the parentheses delineate the arguments to a function.

resetreset · 12-09-2010, 02:59 PM

No no, I know that, I meant how will I know that it's taking str as the argument from (str+= " " + x[indx]) ?

tsg · 12-09-2010, 03:05 PM

The entire expression evaluates to the value of str after the right hand side of the assignment is done.

resetreset · 12-09-2010, 03:10 PM

Sh*t, I didn't know this. Thanks a lot for your help, tsg

tsg · 12-09-2010, 03:51 PM

You're welcome.