I created the below function to generate random number of fix length:
function getRandomNum(length) {
var randomNum =
(Math.pow(10,length).toString().slice(length-1) +
Math.floor((Math.random()*Math.pow(10,length))+1).toString()).slice(-length);
return randomNum;
}
This will basically add 0's at the beginning to make the length of the number as required.