How to prepend a zero in front of any number below 10 in Javascript using Regexp

Question

Good day,

Is there a Regex that I could use to prepend a 0 before any number that is below 10?

I am not looking for a date parsing library, ternary or if/else solutions. (hopefully)

var currentDate = new Date(),
    stringDate = currentDate.getFullYear() + "-" + currentDate.getMonth() + "-" + currentDate.getDate() + " " + currentDate.getHours() + ":" + currentDate.getMinutes() + ":" + currentDate.getSeconds();

    alert( stringDate ); //2011-10-17 10:3:7

I would like a RegExp that I could apply to stringDate to get 2011-10-17 10:03:07

Thank you very much!

Answer 1

Just add the leading 0 every time, then use slice(-2) to get the last two characters, like so:

('0' + currentDate.getHours()).slice(-2)

Answer 2

The following function will allow you to declare a minimum length for a number along or within a string and will pad it with zeros to make it the appropriate length.

var PrependZeros = function (str, len, seperator) {
    if(typeof str === 'number' || Number(str)){
        str = str.toString();
        return (len - str.length > 0) ? new Array(len + 1 - str.length).join('0') + str: str;
    }
    else{
        for(var i = 0,spl = str.split(seperator || ' '); i < spl.length; spl[i] = (Number(spl[i])&& spl[i].length < len)?PrependZeros(spl[i],len):spl[i],str = (i == spl.length -1)?spl.join(seperator || ' '):str,i++);
        return str;
    }
};

For those wanting a less cryptic version

var PrependZeros = function (str, len, seperator) {
    if (typeof str === 'number' || Number(str)) {
        str = str.toString();
        return (len - str.length > 0) ? new Array(len + 1 - str.length).join('0') + str : str;
    }
    else {
        var spl = str.split(seperator || ' ')
        for (var i = 0 ; i < spl.length; i++) {
            if (Number(spl[i]) && spl[i].length < len) {
                spl[i] = PrependZeros(spl[i], len)
            }
        }
        return spl.join(seperator || ' ');
    }
};

Examples:

PrependZeros("1:2:3",2,":"); // "01:02:03"
PrependZeros(1,2); // "01"
PrependZeros(123,2); // "123"
PrependZeros("1 2 3",3); // "001 002 003" 
PrependZeros("5-10-2012",2,"-"); //"05-10-2012"

Answer 3

You don't need regex for that. You can make a simple pad function yourself:

function pad(n) {
    if (n < 10)
        return "0" + n;
    return n;
}

alert(pad(8));
alert(pad(11));

http://jsfiddle.net/DwnNG/

Answer 4

I now this is old, but I just saw this simple and clean solution used on the w3c and just had to share it somewhere.

var hours = currentDate.getHours();
(hours < 10 ? '0' : '') + hours;