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I'm making a function that takes the date a page was last edited, accessed through MediaWiki's API, compares it to the current date, and returns how long ago the page was edited, e.g. 1 year/2 days/etc.

It's essentially a massive if/else statement, and I was wondering if there was a better way to implement it.

var timestamp, utcArr, today, utcArr = [], timestamp2, timestamp3, timestamp4, i, mwArr = [], lastEdited; today = new Date(); utcArr.push(today.getUTCFullYear()); utcArr.push(today.getUTCMonth() + 1); // returns value 0-11 utcArr.push(today.getUTCDate()); utcArr.push(today.getUTCHours()); utcArr.push(today.getUTCMinutes()); /** * Time function * For formatting the returned value for timestamp * example timestamp var: '2013-04-27T14:29:53Z' */ function time() { timestamp2 = timestamp.replace(/(\:|T|Z)/g, '-'); // use g to replace every occurrence, not just one timestamp3 = timestamp2.split('-'); timestamp4 = timestamp3.filter(function (e) { // remove what's left from Z return e; }); for (i = 0; i < timestamp4.length; i++) { mwArr.push(parseFloat(timestamp4[i])); } /** * Compares dates in array and produces the difference between them * @todo Find a better way to do this */ if ((utcArr[0] - mwArr[0]) === 0) { // years if ((utcArr[1] - mwArr[1]) === 0) { // months if ((utcArr[2] - mwArr[2]) === 0) { // days if ((utcArr[3] - mwArr[3]) === 0 { // hours if ((utcArr[4] - mwArr[4]) === 0) { // minutes lastEdited = '1 minute'; } else { lastEdited = utcArr[4] - mwArr[4] + ' minutes'; } } else if ((utcArr[3] - mwArr[3]) === 1 && (utcArr[4] - mwArr[4]) < 59) { lastEdited = utcArr[4] - mwArr[4] + ' minutes'; } else if ((utcArr[3] - mwArr[3]) === 1) { lastEdited = '1 hour'; } else { lastEdited = utcArr[3] - mwArr[3] + ' hours'; } } else if ((utcArr[2] - mwArr[2]) === 1 && (utcArr[3] - mwArr[3]) < 24) { lastEdited = utcArr[3] - mwArr[3] + ' hours'; } else if ((utcArr[2] - mwArr[2]) === 1) { lastEdited = 1 day } else { lastEdited = utcArr[2] - mwArr[2] + ' days'; } } else if ((utcArr[1] - mwArr[1]) === 1 && (utcArr[2] - mwArr[2]) < 30) { // we'll just use 30 as it's easier than coding in each month individually lastEdited = utcArr[2] - mwArr[2] + ' days'; } else if ((utcArr[1] - mwArr[1]) === 1) { lastEdited = '1 month'; } else { lastEdited = utcArr[1] - mwArr[1] + ' months'; } } else if ((utcArr[0] - mwArr[0]) === 1 && (utcArr[1] - mwArr[1]) < 12 ) { lastEdited = utcArr[1] - mwArr[1] + ' months'; } else if ((utcArr[0] - mwArr[0]) === 1) { lastEdited = '1 year' } else { lastEdited = utcArr[0] - mwArr[0] + ' years'; } // empty the array or everything turns out the same mwArr.length = 0; }

The time function is used about half a dozen times within an AJAX request which returns the edit date in the format "2013-04-27T14:29:53Z" which is used in the function to return lastEdited which is then appended to various ids in a table. I've yet to add complete support for 1 day/month/etc. but that'll just be adding in more if/else statements.

I did consider nested switch statements, but wasn't quite sure how to go about it.

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  • \$\begingroup\$ Take a look at this similar question. \$\endgroup\$ Commented May 4, 2013 at 13:04

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I looked at the source code of moment.js for inspiration:

http://momentjs.com/

And I'm trying to be as declarative as possible, using data to define the time-units I want to use:

unitMillisecondFactors = { 'Millisecond': 1000, 'Second': 60, 'Minute': 60, 'Hour': 24, 'Day': 356, 'Year': 10, 'Decade': 1 };

The Javascript Date object can compute the difference between two timestamps in milliseconds. Looking at such a difference the algorithm goes like this: we currently have units Milliseconds. The factor for getting from milliseconds to seconds is 1000. is the number we'er looking at smaller then that factor? Then we're done, we return a result by rounding down and appending the unit. If we're not done, then we devide the number by the factor and try with the next unit. 

function compute_time(timestamp) { var n = new Date() - new Date(timestamp); for (var unit in unitMillisecondFactors) { var factor = unitMillisecondFactors[unit]; if (n < factor) { n = Math.floor(n); if (n == 1) { return s + "more than " + n + " " + unit + " ago\n"; }  else { return s + "more than " + n + " " + unit + "s ago\n"; } } n = n / factor; } }

That's it. See http://jsfiddle.net/bjelline/S23V2/ for a working example with some extra output to see the steps of computation.

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