Recursive functions Js

Question

I have numbers array, through my_number function I create a random numer, if it already exist in the array, I call the function again and create a new random number, if it is not in the array I send it to it through push.

Unfortunately it sems to send all numbers again and again until browser crashes.

How could I fix this.

Thanks for your help

var numbers = [1,2,3,4,5];

function mainFunction(){
    function my_number(){
        var randomNumber = Math.floor((Math.random()*7)+1);
        for(let i=0; i<numbers.length; i++){
            if(numbers[i] === randomNumber){
                my_number();
            }else{
                numbers.push(randomNumber);
            }
        }
    }
    
    my_number();
}

mainFunction();

Every time you push another number onto the array, numbers.length changes. — Pointy
– Pointy, Commented Oct 5, 2020 at 2:55
I already changed i for numbers[i] and I get this in console : Maximum call stack size exceeded — J P
– J P, Commented Oct 5, 2020 at 3:00
@JP You can use numbers.includes(randomNumber). The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate. — Bishan
– Bishan, Commented Oct 5, 2020 at 3:10
Checking for duplicates doesn't come for free. And you want most numbers out of a given set of numbers. That means the further you progress, the more duplicates will you probably generate, and the slower you will progress. A better approach here would be to generate a list with all possible values, shuffle it and then take the first n values from that shuffled list. — Thomas
– Thomas, Commented Oct 5, 2020 at 6:59

Derek Wang · Accepted Answer · 2020-10-05 03:07:06Z

In my_number function, you have called my_number again inside for-loop and it is needed to call my_number function with the result of the for-loop.

So it is needed to get the result if the randomNumber has existed or not through for-loop and based on that, you need to decide to call the function again or not.

Preferred Way

const numbers = [1,2,3,4,5];

function mainFunction(){
  function my_number(){
    const randomNumber = Math.floor((Math.random()*7)+1);
    const isExisted = numbers.some((item) => item === randomNumber);
    if (isExisted) {
      my_number();
    } else {
      numbers.push(randomNumber);
    }
  }
  my_number();
}

mainFunction();
console.log(numbers);

Regarding your CodeBase.

const numbers = [1,2,3,4,5];

function mainFunction(){
  function my_number(){
    const randomNumber = Math.floor((Math.random()*7)+1);
    let isExisted = false;
    for (let index = 0; index < numbers.length; index ++) {
      if (numbers[index] === randomNumber) {
        isExisted = true;
        break;
      }
    }
    if (isExisted) {
      my_number();
    } else {
      numbers.push(randomNumber);
    }
  }
  my_number();
}

mainFunction();
console.log(numbers);

Skylar · Accepted Answer · 2020-10-05 03:10:36Z

There are quite a few problems with the code.

As Pointy pointed out, i should be numbers[i] to compare the array element instead of the index.
You have a function definition inside another function, which is fine, but the only thing the outer function does is call the inner function, so it's redundant.
numbers.push(randomNumber) should be done outside the for loop because it would otherwise only check if randomNumber matches the first element and ignores the rest.
After the call to my_number in the for loop, you need a return statement to prevent the loop from continuing after detecting failure.

var numbers = [1,2,3,4,5];

function my_number() {
    var randomNumber = Math.floor((Math.random() * 7) + 1);
    for(let i = 0; i < numbers.length; i++){
        if (numbers[i] === randomNumber){
            my_number();
            return;
        }
    }
    numbers.push(randomNumber);
}

my_number();

console.log(numbers);

Bishan · Accepted Answer · 2020-10-05 03:58:51Z

This question should include more details and clarify the problem. According to given details, Please check the following answer.

// I have numbers array
var numbers = [1, 2, 3, 4, 5];

function mainFunction() {
    // through my_number function  
    function my_number() {
        // I create a random numer
        var randomNumber = Math.floor((Math.random() * 7) + 1);

        var isExists = numbers.includes(randomNumber);

        // if it already exist in the array
        if (isExists) {
            // I call the function again
            my_number();
        } else { // if it is not in the array
            // I send it to it through push
            numbers.push(randomNumber);
        }

    }

    my_number();
}

mainFunction();
console.log(numbers);

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