javascript generate a number of a variable length

Question

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Generating random numbers in Javascript in a specific range?

If I input a length of say 4, I need to get back a number between 0 9999.

And I want it to be 0 padded (0004), but that may be another function.

For padding the number see http://stackoverflow.com/questions/1267283/how-can-i-create-a-zerofilled-value-using-javascript — Nathan Koop, Aug 10 '12 at 19:40

jeremy · Answer 1 · 2012-08-10T19:49:02.847

for(var x = 5, i = 0, y = ""; i < x; ++i, y += "9");
Math.floor(Math.random()*parseInt(y)); //random number

In the for loop, x would be your input length. You could move the definition of x outside the loop also if you needed.

You could also try this and see which one runs faster (probably the first one, fyi):

for(var x = 5, y = "", i = 0; i < x; ++i, y += Math.floor(Math.random()*9));
parseInt(y); //random number

score 1 · Answer 2 · edited May 23 '17 at 12:02

1

Try this:

function getNumber(range){
var max = Math.pow(10,range);

var num = Math.Random() * max;
}

As for the zerofill you're better off trying what Nathan suggested on his comment this

edited May 23 '17 at 12:02

Community

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answered Aug 10 '12 at 19:46

Isaac Gonzalez

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score 1 · Answer 3 · answered Aug 10 '12 at 19:55

1

function getRandom(c){
    var r = (Math.random() * Math.pow(10, c)).toFixed(0);
    while(r.length != c)
        r = "0" + r; 
    return r;
}

getRandom(3);

answered Aug 10 '12 at 19:55

Diode

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This is a nice solution, works well and has the 0 padding built in. Thanks! – skeddles Aug 10 '12 at 20:19

score 0 · Answer 4 · edited May 23 '17 at 10:34

Since it's javascript, you may want to take advantage of its weak typing in this scenario. One particular hackerish way of doing this is to generate n numbers between 0-9 and use string concatenation.

This post seems to have the answer: JavaScript expression to generate a 5-digit number in every case and you can pad with concatenation.

EDIT: so here is my implementation of it:

function random(x){
  var rand = Math.floor(Math.random() * Math.pow(10,x));
  var dummy = rand;
  while (dummy<Math.pow(10,x-1)){
    rand = "0" + rand;
    dummy = dummy*10;
  }
  return rand;
}

Phillip Schmidt · Answer 5 · 2012-08-10T19:55:58.217

0

Well, here's the number part. You can probably figure out the padding part.

function makeNumber(number){
    var nines = "";
    var returnNumber = "";
    for(var i = 0; i < number; i++)
    {
         nines+= "9";  
    }
    for(var i = 0; i < number; i++)
    {
        var returnNumber += String(Math.Random() * parseInt(nines));
    }
    return returnNumber;
}

edited Aug 10 '12 at 19:55

answered Aug 10 '12 at 19:48

Phillip Schmidt

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this could easily be done with 1 for loop and no statements in between the curly brackets, look at my solution below. – jeremy Aug 10 '12 at 19:51
@Nile yeah, I saw that. Nice thinking. – Phillip Schmidt Aug 10 '12 at 19:52
@Nile though in this case, we're talking about reeeeeally negligible time wasted, and I think its a lot more clear to read this way – Phillip Schmidt Aug 10 '12 at 19:53
@PhillipSchmidt, what's with the declaration of "i" using `int`? Is that valid? – jeremy Aug 10 '12 at 19:54
@Nile lol i meant to take that out as part of an edit, but then i cancelled my the edit. editing it now. (note that it's because I've spent all day writing c# code, lol) – Phillip Schmidt Aug 10 '12 at 19:55
@PhillipSchmidt too much C lately probably... lol (posted this before I read your parenthesis) – jeremy Aug 10 '12 at 19:56

score 0 · Answer 6 · answered Aug 10 '12 at 20:02

Kind of sloppy but works:

var length = 4; //<-- or get however you want
var big = "";
for (i=0; i<length; i++) {
    big = big + "9";
}
var big = parseInt(big);
var random = Math.floor(Math.random() * big).toString();
var random_len = random.toString().length;
if (random_len < length) {
    var random_padded = random.toString()
    padding = length - random_len;
    for (i=0; i<padding; i++) {
        random_padded = "0" + random_padded;
    }
    random = random_padded
}
alert(random);

javascript generate a number of a variable length

6 Answers6