Javascript generate random string

// Generate a random alphanumerical string of length 11 ( change substring parameter for other length)
Math.random().toString(36).substring(2);

function getRandomString(length) {
    var randomChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    var result = '';
    for ( var i = 0; i < length; i++ ) {
        result += randomChars.charAt(Math.floor(Math.random() * randomChars.length));
    }
    return result;
}

//usage: getRandomString(20); // pass desired length of random string

function randomString(length) {
		var result           = '';
		var characters       = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789~!@#$%^&*()_+=-';
		var charactersLength = characters.length;
		for ( var i = 0; i < length; i++ ) {
		   result += characters.charAt(Math.floor(Math.random() * charactersLength));
		}
		return result;
	 }
randomString(4);

const string_length = 10
[...Array(string_length)].map(i=>(~~(Math.random()*36)).toString(36)).join('')

 Math.random().toString(36).substring(2, 15) + Math.random().toString(36).substring(2, 15);