Array Replication Function in JavaScript using self-executing inner function

Question

I'm trying to write an array replication function in JavaScript that will take an array and a replication factor as input parameters, and return that replicated array.

Like such:

expect(replicate([2,3,4],2).toEqual([2,3,4,2,3,4]));

And I'm trying to accomplish this with a recursively-called, self-executing inner function that should return the desired value to the outer function when finished.

The inner function seems to work correctly:

var replicate = function (inputArray, n) {
    var outputArray = [];
    return (function replicateInner(n) {
        if (n > 0) {
            outputArray.push(inputArray.slice(0));
            replicateInner(--n)
        } else {
            alert('inner function returns: ' + outputArray);
            //inner function returns: [2,3,4,2,3,4]
            return outputArray;
        }
    })(n);

 };

But when I call the outer function, it returns undefined

alert(replicate([2,3,4],2)); // returns undefined, not [2,3,4,2,3,4]

Any idea what I might be missing here? Thanks!

thefourtheye · Accepted Answer · 2014-03-27 18:34:00Z

4

Because you are not returning the result from replicateInner(--n), like this

return replicateInner(--n);

Also, when you push the inputArray.slice(0) to outputArray, the result will be like this

[ [ 2, 3, 4 ], [ 2, 3, 4 ] ]

What you need to do is to concatenate the arrays like this

outputArray = outputArray.concat(inputArray.slice(0));

with this change, the output becomes

[ 2, 3, 4, 2, 3, 4 ]

answered Mar 27, 2014 at 18:34

thefourtheye

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6 Comments

David Byman Over a year ago

That did it! Thanks! Here's the working fiddle: jsfiddle.net/databass/hX8Qk

thefourtheye Over a year ago

@DavidByman Glad to have been of help! Feel free to accept my answer if you feel it was useful to you. :-)

David Byman Over a year ago

But I do get the same results whether using push or concat.

thefourtheye Over a year ago

@DavidByman Are you sure? When you use .push, you would be getting an array of array.

thefourtheye Over a year ago

@DavidByman Correct, you are getting two arrays, right? But you don't want that.

|

Jess · Accepted Answer · 2014-03-27 19:20:51Z

1

Awesome question. Here is a simplified answer that has both an IIFE and the recursion. We don't need to pass anything around or pass anything to the IIFE since it is all in closure scope.

var replicate = function (inputArray, n) {
    var outputArray = [];
    (function replicateInner() {
        if (n > 0) {
            outputArray = outputArray.concat(inputArray.slice(0));
            --n;
            replicateInner()
        }
    })();
    return outputArray;
};

edited Mar 27, 2014 at 19:20

answered Mar 27, 2014 at 19:11

Jess

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1 Comment

David Byman Over a year ago

this is much cleaner. Thanks!

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