Custom moment formats based on string length

Just wanted to gage how solid this code is. With moment cracking down on lazy formatting I thought this was a good way to parse the string for what format to use.

var string = $this.attr("data-date");
var withoutTime = "YYMMDD";
var withTime = "YYMMDDHHmm";
var format = function(){
  if(string.length == withoutTime.length) return withoutTime;
  if(string.length == withTime.length) return withTime;
  return false;
}();
var date = moment(string, format);

How about this (based on the assumption that $ refers to jQuery):

var dateString = $('div').data('date');

function getDateFormat(dateString){

    if(!dateString) return false;

    var dateTimeFormats = ['YYMMDD' ,'YYMMDDHHmm'];

    return dateTimeFormats.filter(function(format){
        return format.length === dateString.length;
    })[0] || false;
}

console.log(getDateFormat(dateString));

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jQuery's data() method is preferred over attr() since it's intended to be used with either html5 data attributes (like in your case) or for caching data in the jQuery $.cache.

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Try to use more descriptive names and don't use reserved keywords as variable names (or a close call like string vs String in your case).

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Check if the date string is defined before making use of it

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I suggest that you always do equality checks using the identity operator, ===. Otherwise you might get results like 1 == true since the type is not taken in to consideration

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If you want to use Array.prototype.filter in IE

http://jsfiddle.net/zb4sfno3/

StackExchange Code Review Q#73363, answer score: 3