generate 4 digit random number using substring

Question

I am trying to execute below code:

var a = Math.floor(100000 + Math.random() * 900000);
a = a.substring(-2);

I am getting error like undefined is not a function at line 2, but when I try to do alert(a), it has something. What is wrong here?

Solution 1

That's because a is a number, not a string. What you probably want to do is something like this:

var val = Math.floor(1000 + Math.random() * 9000);
console.log(val);

• Math.random() will generate a floating point number in the range [0, 1) (this is not a typo, it is standard mathematical notation to show that 1 is excluded from the range).
• Multiplying by 9000 results in a range of [0, 9000).
• Adding 1000 results in a range of [1000, 10000).
• Flooring chops off the decimal value to give you an integer. Note that it does not round.

---

General Case

If you want to generate an integer in the range [x, y), you can use the following code:

Math.floor(x + (y - x) * Math.random());

Solution 2

This will generate 4-digit random number (0000-9999) using substring:

var seq = (Math.floor(Math.random() * 10000) + 10000).toString().substring(1);
console.log(seq);

Solution 3

I adapted Balajis to make it immutable and functional.

Because this doesn't use math you can use alphanumeric, emojis, very long pins etc

const getRandomPin = (chars, len)=>[...Array(len)].map(
   (i)=>chars[Math.floor(Math.random()*chars.length)]
).join('');


//use it like this
getRandomPin('0123456789',4);

Solution 4

$( document ).ready(function() {
  
    var a = Math.floor(100000 + Math.random() * 900000);   
    a = String(a);
    a = a.substring(0,4);
    alert( "valor:" +a );
  
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>

Solution 5

$(document).ready(function() {
  var a = Math.floor((Math.random() * 9999) + 999);
  a = String(a);
  a = a.substring(0, 4);
});

View more solutions

Comments

[Sumner Evans]

This generates a number with 6 digits rather than 4.

[Felix Kling]

It also doesn't create a number but a string.

[Felix Kling]

Your demo clearly shows that your solution produces a string of length 6.

[Shelly]

yeah thats what i am trying to do

[Felix Kling]

Well, the OP wants to create a 4 digit number.

[Isaac Stevens]

got to remember that when you do a math logic you problably will receive a data type as either int or double, therefore you got to convert the result to string to be handle by the substring function, hope this helps

[Felix Kling]

How is this different from erkaner's solution? The $(document).ready call is unnecessary here.

[Isaac Stevens]

Thats in case you use it in jquery code, but you are right otherwise is unnecessary

[5ervant - techintel.github.io]

I can't regenerate a code that starts with a zero, such as 0123.

[Sumner Evans]

@5ervant, that would be a 3 digit number. (Mathematically, the leading 0 does not matter.)

[Balaji Ts]

it will generate random value from char variable with length 5 & in loop it will check the length and generate random 5 digit value from char variable and convert it to uppercase