# How to add leading zeros to the result of a date difference calculation, using moment.js?

One of the charms of the moment.js library is the perfect way it deals with sometimes having 366 days in a year 😉 and the varying length of monthes.

So I have assembled the following piece of code:

```<script src='https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.3/moment.js' type='text/javascript'></script>
<script type="text/javascript">

Date.getFormattedDateDiff = function(date1, date2) {
var b = moment(date1),
a = moment(date2),
intervals = ['years','months','weeks','days','hours','minutes','seconds'],
out = [];

for(var i=0; i<intervals.length; i++){
var diff = a.diff(b, intervals[i]);
b.add(diff, intervals[i]);
out.push('<div>' + diff + ' ' + intervals[i] + '</div><br/>');
}
return out.join(' ');
};

window.onload = function calculateInterval() {
var start = moment("2013-09-04"),
end   = moment();

document.getElementById('output').innerHTML
= 'Time elapsed between "' + start.toISOString().split('T')
+ '" and "' + end.toISOString().split('T') + '":<br/><br/>'
+ Date.getFormattedDateDiff(start, end);
}
</script>

<p><label id="output"></label></p>
```

A codepen can be found here …

Probably you will immediately notice that I am missing the leading zeros in the result. I have tried several formatting-efforts. But unfortunately, all of them don’t seem to work.

Any suggestions how to get the leading zeros in the result, so 07 years instead of 7 years, etc. are highly appreciated.

## Answer

Simple if statement to prepend a 0 will work — `typeof` diff() value returns `number` and you need to convert to a string to manipulate.

```Date.getFormattedDateDiff = function(date1, date2) {
var b = moment(date1),
a = moment(date2),
intervals = ['years','months','weeks','days','hours','minutes','seconds'],
out = [];

for(var i=0; i<intervals.length; i++){
var diff = a.diff(b, intervals[i]);
b.add(diff, intervals[i]);
if (diff.toString().length == 1) {
diff = "0" + diff.toString();
}
out.push('<div>' + diff + ' ' + intervals[i] + '</div><br/>');
}
return out.join(' ');
};

window.onload = function calculateInterval() {
var start = moment("2013-09-04"),
end   = moment();

document.getElementById('output').innerHTML
= 'Time elapsed between "' + start.toISOString().split('T')
+ '" and "' + end.toISOString().split('T') + '":<br/><br/>'
+ Date.getFormattedDateDiff(start, end);
}
```

You can also refer to this thread for some fantastic leading 0 methods.