Replace Loops With Recursion

JavaScript
1

Hi,

I’m working my way through the JavaScript source and I’m currently at the “Replace loops with recursion” part of the JavaScript course.

I wanted to really understand so got more help from the video.
I took this code that Beau uses to help understand recursion:

function countdown(i) {
    console.log(i); if (i <= 1) {  // base case
        return;
    } else {     // recursive case
        countdown(i-1);
    }
}

countdown(5);    // This is the initial call to the function.

First of all my question is how come I cannot use countdown(i–) instead?
I guess from previous lessons, it seems to do the same “decrements by 1” but i think its causing an infinite loop.

Second of all, the code above is simple enough but i thought if i were to fiddle around to get the same result, is it still recursion?
like below:

function countdown(i) {
    console.log(i); 
        if (i > 1) { // Recursive case
            countdown(i-1);
    } else {
        return // Base case
    }
}

countdown(5);

the second code looks easier to understand to me but if its not exactly the same thing as the first example then i guess, that’d be good to know lol

2

i-- wil decrease i but returns the previous value, so you are passing i in the function, without reducing it first.

note that without a return statement also there, the function will return undefined

it is recursion as long the function call itself, so also your second version is recursion

3

Ok thank you. After you said this > " i-- wil decrease i but returns the previous value"
I remembered something from before. So changed it to countdown(–i) which works :slight_smile:

Thanks for lending me your brain power :smiley:

4

you still don’t need to change the value of i, as if you need a bit more complex logic there that still need the same value of i, you will have unexpected behaviour

5

ah i see, okay thanks. I’ll remember that :slight_smile: