Recursive reduce in JavaScript

Question

I'm quite new to JavaScript and don't understand a few of its behaviours. I want to write a recursive version of reduce function found in Eloquent JavaScript book. That's my code:

function rec_reduce( fn, base, list ) {
 if( list.length === 0 ) {
 return base;
 }
 else {
 rec_reduce( fn, fn( base, list[ 0 ] ), list.slice( 1 ) );
 }
}
print( rec_reduce( Math.min, 100, [ 5, 3, 7, 2, 6, 5 ] ));

The result was:

undefined

To see what's going on I put:

print( base );

as a first line of the function and the result was:

100
5
3
3
2
2
2
undefined

Whould anyone explain me why?

Answer 1

In that else block, you'll have to

return rec_reduce( ... )

• trzewiczek: THX A LOT!! I forget about this return thing now and then mainly because every thime I need something recursive I prototype it in Scheme - there's no return statement ;) Thx again!
• Linus Kleen: @trzewiczek Care to accept, then? Suits your profile well, too.
• trzewiczek: Sorry about that - it's just I'm not experienced - forgot about that!!

Answer 2

Another way to do it:

reduce_file.js:

function reduce(arr, func, initv){
 if(arr.length) return reduce(arr.slice(1), func, func(initv, arr[0]))
 else return initv
}
module.exports = reduce

and then you use it as:

reduce = require('./reduce_file.js')
console.log(reduce([1,2,3,4], function(prev, curr) {
 return prev + curr
}, 0))

result:

10 

from 1+2+3+4=10