CODEWITHSUNDEEP
javascriptrecursion
3gwebtrain
3gwebtrain

Reputation: 15299

How this function works with array without a loop?

Here is my sample function.

    let array = ["x", "y", "z", 4, 5];
    
    function print(arr, pos, len) {
      if (pos < len) {
        console.log(arr[pos]);
        print(arr, pos + 1, len);
      }
      return;
    }
    print(array, 0, array.length);

The array prints each one by one. But how this is happening without a loop? any one clarify to understand the function process here?

Upvotes: 1

Views: 1014

Answers (3)

Nick Parsons
Nick Parsons

Reputation: 50854

How is this happening without a loop?

It is using recursion, this means the function itself is called from within the function. Using a loop is not the only way to iterate over a collection.

If you look at your code the print function is called once outside your function, but also inside the print function itself. So when we first run your function with the array [1, 2, 3] we run the function with the following arguments:

print([1, 2, 3], 0, 3)

Then when we enter the function, we look at the if statement and see that pos (0) is in fact less than len (3). So, we then go ahead and console.log(arr[0]) which will print the first item in your array.

We then proceed to the next line, and call print again, but this time from within the function. We now call it with the following arguments:

print([1, 2, 3], 1, 3)

This, again, will go through and look at the if statement, see that it is true, and run console.log(arr[1]). Once again, we will call print with the following arguments:

print([1, 2, 3], 2, 3)

This will then console.log(arr[2]) (the last item in the array) and again call print with the following arguments:

print([1, 2, 3], 3, 3)

however, this time, our if statement is not met / not true, as pos (3) is not less than len (3). In other words, our base case (the condition to stop the recursion) is met. So, what we do instead of printing is return.

Doing a return will take us back to where we last called our print statement, this means we will go back to inside the if statement from our previous call to print and then return again once the if statement is complete. This unravelling process continues until we return to our original call of print (outside the print function declaration). Our program then terminates after this as there is no more code to run.

Upvotes: 3

Akrion
Akrion

Reputation: 18525

The process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called as recursive function

In your scenario this means that print is called multiple times from inside its function body to print the array contents.

let array = ["x", "y", "z", 4, 5];

function print(arr, pos, len) { // <-- notice current position is passed as parameter
  if (pos < len) {              // <-- keep doing it until end of the array
    console.log(arr[pos]);      // <-- prints to the console the value at current position
    print(arr, pos + 1, len);   // <-- print function is called again with dif. pos!
  }
  return;
}
print(array, 0, array.length);  // <-- call the print function with 0 and 5 as parameters

Upvotes: 1

Sachin Sarola
Sachin Sarola

Reputation: 1041

It is a recursive function:

Read blog it is to simple and very effective: click Here

Upvotes: 1

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