用Java的递归函数填充数组？

Question

I am trying to fill an array with ranges of values in a recursive function, but i see a weird thing happening while returning the array, though the array has values, when i alert it outside the function it gives me undefined. Not Sure whether its my code issue or any kind of behavior.

Same implementation when i tired using simple for loop it worked fine.

I don't know what title to give for this problem, please suggest me a good one.

JS Fiddle

With Recursion

var arr = [];
function fillArray(n,i){
    if(arr.length !== n){
        if(i===0)
            arr[i] = i;
        else
            arr[i] = arr[i-1] + 1;
        fillArray(n,++i);
    }
    else{
         console.log(arr);
         return arr;
    }
}
console.log(fillArray(10,0));

With For Loop

var arr = [];

function fillArray(start,end){
    for(var i=start,j=0;i<=end;i++,j++){
        arr[j] = i;
    }
    return arr;
}

alert(fillArray(1,10));

Answer 1

 function fillArray(n, i, a) { a.push(i); return a.length < n ? fillArray(n, ++i, a) : a; } console.log(fillArray(10, 0, [])); 

Answer 2

First, this is not a good example of something that should be implemented recursively in JavaScript. It's unidiomatic.

The reason the result is undefined outside the function is that your code fails to return the result of each successive recursive call. The recursion statement should look like:

    return fillArray(n,++i);

Without that, the final call that does return the array will have its return value simply ignored by the penultimate call.

Answer 3

Take a look on your example:

var arr = [];
function fillArray(n,i){
    if(arr.length !== n){
        if(i===0)
            arr[i] = i;
        else
            arr[i] = arr[i-1] + 1;
        fillArray(n,++i); // ends without returning anything
    }
    else{
         console.log(arr);
         return arr; // return array
    }
}
console.log(fillArray(10,0));

First of all I wouldn't declare value outside function and I wouldn't do with recursion (as you pollute your closure. But if you do so and you keep your function as it is, don't expect value as return here (as you edit variable outside of it).

var arr = [];
function fillArray(n,i){
    if(arr.length !== n){
        if(i===0)
            arr[i] = i;
        else
            arr[i] = arr[i-1] + 1;
        fillArray(n,++i);
    } // return not needed
}
fillArray(10,0);
console.log(arr);