Random “month & day” with JS

Can anyone review this?

setInterval(function() {
var days_array = [31,29,31,30,31,30,31,31,30,31,30,31];
var m = randNum(12);
var m_limit = days_array[m-1];
var d = randNum(m_limit);
$("code").html("day = "+d+"<br>month = "+m); },1000); function randNum(limit){var r=Math.floor(Math.random()*limit)+1;return r;}  jsFiddle 4 Answers function randomMillisecond() { return Math.floor(Math.random() * 1000 * 60 * 60 * 24 * 365.25); } setInterval(function() { var date = new Date(randomMillisecond());$("code").html("day = " + date.getDate() + "<br>month = " + date.getMonth());
}, 1000);


If you don't need 02/29.

function randNum(limit){var r=Math.floor(Math.random()*limit)+1;return r;}


Can be shortened to:

function randNum(limit){return Math.floor(Math.random()*limit)+1;}


You should also declare your variables outside of the setInterval and then set them inside only if you need to (for example, the days_array never changes so only needs to be decalared once and not every second.

This is biased towards days in shorter months. If you want every day to be equally likely you should choose a random number from 1 to 365 (366 for leap years) and calculate the day and month from that.

I would reduce the visibility of the variables so they won't get overwritten by accident and I'd separate the date creation from displaying them. Like this, for example:

var datePasser = function(callback) {
var randNum = function(max) {
return Math.floor(1 + Math.random() * max);
},
daysInMonth = [31,29,31,30,31,30,31,31,30,31,30,31];
return function() {
var month = randNum(12),
date = randNum(daysInMonth[month - 1]);
callback(month, date);
}
},
printRandomDate = datePasser(function(month, date) {
\$('code').html("day = "+date+"<br>month = "+month);
});
setInterval(printRandomDate, 1000);​