Javascript - Generate random number between 0000 to 9999

I want to generate random numbers between 0000 to 9999. But my problem was prefix zero gets ignored. I can't able to print exactly 4 numbers, Sometimes it becomes 3 numbers or 2 numbers.

I tried using below code

Math.floor(0000 + Math.random() * 9000);

If number is 791 then it should be 0791, If number is 56 then it should be 0056.