Generate a random 4 digit number with no repeating digits

Question

I have this function to create a random 4 digit number:

    generateCode = function(){
      var fullNumber = [];
     var digit1 = Math.floor(Math.random() * 9) + 1;
     var digit2 = Math.floor(Math.random() * 9) + 1;
     var digit3 = Math.floor(Math.random() * 9) + 1;
     var digit4 = Math.floor(Math.random() * 9) + 1;
     fullNumber.push(digit1, digit2, digit3, digit4);
     this.theCode(fullNumber.join("")) ;
    }

But I need to create a 4 digit random number with no repeating digits.

So "1234" or "9673". But not "1145" or "5668"

Is there an efficient way to do this?

Answer 1

You can use this handy shuffle function to shuffle an array containing the numbers, and pick the first 4.

function random4Digit(){
  return shuffle( "0123456789".split('') ).join('').substring(0,4);
}

function shuffle(o){
    for(var j, x, i = o.length; i; j = Math.floor(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
    return o;
}

alert( random4Digit() );

Edit: If you actually want a Number not starting with 0:

function random4DigitNumberNotStartingWithZero(){
    // I did not include the zero, for the first digit
    var digits = "123456789".split(''),
        first = shuffle(digits).pop();
    // Add "0" to the array
    digits.push('0');
    return parseInt( first + shuffle(digits).join('').substring(0,3), 10);
}

function shuffle(o){
    for(var j, x, i = o.length; i; j = Math.floor(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
    return o;
}

alert( random4DigitNumberNotStartingWithZero() );