How to create random string in javascript

Well this article is inspired by my article on how to create random string in mysql

I love to simplify all small things into one function. So i am back with an another one.

Nice ingredients make food delicious, same in any language, best use of core functions will make your function useful and efficient.

Ingredients

• toLowerCase()
• substr()
• Math.floor()
• Math.random()

Step 1

generate one random string between 1 to n number.

var length = 8;
Math.floor(Math.random() * length) + 1;
// this will return random number between 1 to 8

Step 2

We will use above random number to get one random string.

substr function expect 2 parameter substr(start-index,length)

var string = "onlinegurucool";
var randomDigit = Math.floor(Math.random() * string.length) + 1;
var substr_limit = 1; //this should be one for this recipe
string.substr(randomDigit, substr_limit);
// this will return any random word from given string

Step 3

now we have to loop for how long random string length we need

var string = "onlinegurucool";
var randomDigit = Math.floor(Math.random() * string.length) + 1;
var substr_limit = 1; //this should be one for this recipe
var length = 6; // random string length 
var result = "";
// loop till length 
for (let i = 1; i <= length; i++) {
    result += string.substr(randomDigit, substr_limit);
}

now lets combine all this into reusable function. and garnish with one last thing that is toLowerCase(). I am using lower as last parameter on my function which is initially false if you make it true you will get result in lowvercase only.

// define function
function generateRandomString(
    length = 1,
    string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
    lower = false
) {
    var result = "";
    string = lower ? string.toLowerCase() : string;
    for (let i = 1; i <= length; i++) {
        result += string.substr(
            Math.floor(Math.random() * string.length) + 1,
            1
        );
    }
    return result;
}
// calling function
generateRandomString(5); // result N2GOH,15010,B6ESI
//with custom string
generateRandomString(5, "ONLINEGURUCOOL"); // result RLENIE,LENUO,EGNOCC
// with custom string and lower case true
generateRandomString(5, "ONLINEGURUCOOL", true); // result ngcceu,golll,gounoo