使用子字符串生成 4 位随机数

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?

Answer 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());

Answer 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);

Answer 3

 $( 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>

Answer 4

Your a is a number. To be able to use the substring function, it has to be a string first, try

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

Answer 5

You can get 4-digit this way .substring(startIndex, length) , which would be in your case .substring(0, 4) . To be able to use .substring() you will need to convert a to string by using .toString() . At the end, you can convert the resulting output into integer by using parseInt :

 var a = Math.floor(100000 + Math.random() * 900000)
 a = a.toString().substring(0, 4);

 a =  parseInt(a);

 alert(a);

https://jsfiddle.net/v7dswkjf/

Answer 6

The problem is that a is a number. You cannot apply substring to a number so you have to convert the number to a string and then apply the function.

DEMO: https://jsfiddle.net/L0dba54m/

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

Answer 7

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

Answer 8

// It Will Generate Random 5 digit Number & Char 
const char = '1234567890abcdefghijklmnopqrstuvwxyz'; //Random Generate Every Time From This Given Char
const length = 5;
let randomvalue = '';
for ( let i = 0; i < length; i++) {

    const value = Math.floor(Math.random() * char.length);

    randomvalue += char.substring(value, value + 1).toUpperCase();

}

console.log(randomvalue);

Answer 9

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);

Answer 10

    function getPin() {
    let pin = Math.round(Math.random() * 10000);
    let pinStr = pin + '';

    // make sure that number is 4 digit
    if (pinStr.length == 4) {
        return pinStr;
       } else {
        return getPin();
       }
    }

   let number = getPin();

Answer 11

Just pass Length of to number that need to be generated

  await this.randomInteger(4);
  async randomInteger(number) {

    let length = parseInt(number);
    let string:string = number.toString();
    let min = 1* parseInt( string.padEnd(length,"0") ) ;
    let max =   parseInt( string.padEnd(length,"9") );

    return Math.floor(
      Math.random() * (max - min + 1) + min
    )
  }

Answer 12

I've created this function where you can defined the size of the OTP(One Time Password):

generateOtp = function (size) {
    const zeros = '0'.repeat(size - 1);
    const x = parseFloat('1' + zeros);
    const y = parseFloat('9' + zeros);
    const confirmationCode = String(Math.floor(x + Math.random() * y));
 return confirmationCode;
}

How to use:

generateOtp(4)
generateOtp(5)

To avoid overflow, you can validate the size parameter to your case.

Answer 13

Numbers don't have substring method. For example:

 let txt = "123456"; // Works, Cause that's a string. let num = 123456; // Won't Work, Cause that's a number.. // let res = txt.substring(0, 3); // Works: 123 let res = num.substring(0, 3); // Throws Uncaught TypeError. console.log(res); // Error

For Generating random 4 digit number, you can utilize Math.random()

For Example:

 let randNum = (1000 + Math.random() * 9000).toFixed(0); console.log(randNum);

Answer 14

This is quite simple

const arr = ["one", "Two", "Three"]
const randomNum = arr[Math.floor(Math.random() * arr.length)];

Answer 15

export const createOtp = (): number => {
      Number(Math.floor(1000 + Math.random() * 9000).toString());
}