Recursive

Recursion

Recursion is a function calls itself.

Example

One example is the calculation of factorials. The factorial of a number n is calculated by multiplying 1 * 2 * 3 *… n. The following example shows how to calculate factorials iteratively,that is, by using a while loop in which the result is calculated.

    function factorial(num){  
        // If the number is less than 0, reject it.  
        if (num < 0) {  
            return -1;  
        }  
        // If the number is 0, its factorial is 1.  
        else if (num == 0) {  
            return 1;  
        }  
        var tmp = num;  
        while (num-- > 2) {  
            tmp *= num;  
        }  
        return tmp;  
    }  

    var result = factorial(8);  
    console.log(result);// Output: 40320  

You can make the example recursive very simply. Instead of using a while loop to calculate the value, you can simply call factorial again, passing in the next lowest value. The recursion stops when the value is 1.

    function factorial(num){  
        // If the number is less than 0, reject it.  
        if (num < 0) {  
            return -1;  
        }  
        // If the number is 0, its factorial is 1.  
        else if (num == 0) {  
            return 1;  
        }  
        // Otherwise, call this recursive procedure again.  
        else {  
            return (num * factorial(num - 1));  
        }  
    }  

    var result = factorial(8);  
    console.log(result);// Output: 40320