How to generate a random string from ASCII characters in JavaScript

Question

How can I build a simple string generator that creates and prints out a randomized string of 10 characters, including lowercase and uppercase letters, numbers and special characters from 0 to 127 of the ASCII table by typing the ASCII-character-number-range in the method? Not a variable like

    var possibleCharacters = "01234567890abcdefgh....."

A friend of me already built it in Java (see below), so how can I build that in JavaScript, also with a for-loop like in the Java example?

    public class Main {
public static void main(String[] args) {
    for (int counter = 0; counter <= 9; counter++) {
        int randomNum = 0 + (int)(Math.random() * 127);
        if(randomNum > 33) {
            System.out.print((char)randomNum);
        }else {
            counter--;
        }
    }
}
}

It should just generate something like "_e7N?:G&M0" i.e.

@YongQuan Thanks, this looks good. Unfortunately as a newbie I don't have any clue how to write that method. I also don't understand the code of my friend, and why he wrote a 33 in the code. I have no clue how to write that whole password generator function — MrFrontend
– MrFrontend, Commented Sep 12, 2019 at 4:33
Thank you so much @shrys it's working! How can I upvote your comment as it is right below my thread and not in the general answers section? — MrFrontend
– MrFrontend, Commented Sep 12, 2019 at 4:39
@MrFrontend if you are planning to implement a password generator function, you CANNOT generate random string this way because Math.random() is NOT cryptographically secure. You have to use the Web Crypto API. — yqlim
– yqlim, Commented Sep 12, 2019 at 6:13

shrys · Accepted Answer · 2019-09-12 04:43:19Z

1

A function to return the random string:

function getString() {
  var str = "";
  for (counter = 0; counter <= 9; counter++) {
    var randomNum = 0 + parseInt(Math.random() * 127);
    if (randomNum > 33) {
      str += String.fromCharCode(randomNum);
    } else {
      counter--;
    }
  }
  return str;
}
for (i = 0; i < 10; i++)
  console.log(getString());

If you're attempting to generate numbers between 33 and 127:

function getString() {
  var str = "";
  for (counter = 0; counter <= 9; counter++) {
    var randomNum = 0 + parseInt(Math.floor(Math.random() * (127 - 33 + 1) + 33));
    str += String.fromCharCode(randomNum);
  }
  return str;
}
for (i = 0; i < 10; i++)
  console.log(getString());

answered Sep 12, 2019 at 4:43

shrys

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2 Comments

MrFrontend Over a year ago

Thanks again. Can you tell me in the fourth line (of both examples) what the "0" in 0 + parseInt is about? When I delete it, it seems it doesn't change anything.

shrys Over a year ago

Yes I think it doesn't do anything, might as well omit it

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