Some time ago I was asked to build a multi-day date-picking interface that was to accept dates selected from a calendar and display them in a list without making a round-trip to the server. Since this was for a web application with an international audience, I needed to handle different date formats (localization) and languages (translation). Translation was no big deal; we had long ago established the convention of receiving from the server a JSON object with the necessary terms and phrases, populated by resource bundles. But the date formatting was another matter. And since the back-end was in Java, it would be nice to use the same date-formatting strings that the back-end guys were using, to make adding new locales easier. My formatDate() was the result:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 | /** * formatDate() * - follows Java SimpleDateFormat pattern conventions but does not support time zones * - depends on dateLanguage object * * @param dDate a javascript date object * @param patternStr a Java-style date format string * @return string representation of the date */ function formatDate(dDate, patternStr) { /* interior functions */ //countTokenLength() counts the number of repetitions of the individual date format token appearing next in the string function countTokenLength(str) { var re = /^([a-zA-Z])(1){0,100}/g; var matchStr = str.match(re); if (!matchStr) { return 1; } return matchStr[0].length; } //padResult() adds copies of padStr to num until it is as wide as necessary //in retrospect, this could be made much shorter and more efficient function padResult(num, width, padStr) { //dependent function var returnStr = ""; if (width > 1) { var padLength = width - num.toString().length; if (padLength) { for (i=0; i<padLength; i++) { returnStr += padStr; } } } returnStr += num.toString(); return returnStr; } //here is where the action begins var resultStr = ""; var subPatternLength = 0; while (patternStr.length > 0) { subPatternLength = countTokenLength(patternStr); var token = patternStr.substr(0,1); switch (token) { case "G": resultStr += (dDate.getFullYear() >=0) ? dateLanguage.eraNames[1] : dateLanguage.eraNames[0]; break; case "y": var x = dDate.getFullYear().toString(); if (dDate.getFullYear() > 999) { if (subPatternLength > 2) { resultStr += x; } else { resultStr += x.substring(x.length - 2, x.length); } } else { resultStr += x + " " + ((dDate.getFullYear() >=0) ? dateLanguage.eraNames[1] : dateLanguage.eraNames[0]); } break; case "M": if (subPatternLength > 2) { resultStr += (subPatternLength == 3) ? dateLanguage.monthNamesShort[dDate.getMonth()] : dateLanguage.monthNames[dDate.getMonth()]; } else { resultStr += padResult(dDate.getMonth(), subPatternLength, '0'); } break; case "w": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += "[week in year]"; break; case "W": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += "[week in month]"; break; case "D": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += "[day in year]"; break; case "d": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += padResult(dDate.getDate(), resultLength, '0'); break; case "F": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += "[day of week in month]"; break; case "E": switch (subPatternLength) { case 1: resultStr += dateLanguage.weekDayNamesAbbrev[dDate.getDay()]; break; case 2: resultStr += dateLanguage.weekDayNamesTiny[dDate.getDay()]; break; case 3: resultStr += dateLanguage.weekDayNamesShort[dDate.getDay()]; break; default: resultStr += dateLanguage.weekDayNames[dDate.getDay()]; break; } break; case "a": resultStr += (dDate.getHours() < 12) ? dateLanguage.amPmNames[0] : dateLanguage.amPmNames[1]; break; case "H": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += padResult(dDate.getHours(), resultLength, '0'); break; case "k": var resultLength = (subPatternLength >= 2) ? 2 : 1; if (dDate.getHours() == 0) resultStr += "24"; else resultStr +=padResult(dDate.getHours(), resultLength, '0'); break; case "K": var resultLength = (subPatternLength >= 2) ? 2 : 1; var adjust = (dDate.getHours() >= 12) ? -12 : 0; resultStr += padResult((dDate.getHours() + adjust), resultLength, '0'); break; case "h": var resultLength = (subPatternLength >= 2) ? 2 : 1; var adjust = (dDate.getHours() >= 12) ? -12 : 0; if ((dDate.getHours() + adjust) == 0) { resultStr += "12"; } else { resultStr += padResult((dDate.getHours() + adjust), resultLength, '0'); } break; case "m": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += padResult(dDate.getMinutes(), resultLength, '0'); break; case "s": var resultLength = (subPatternLength >= 2) ? 2 : 1; resultStr += padResult(dDate.getSeconds(), resultLength, '0'); break; case "S": resultStr += dDate.getTime(); break; case "z": resultStr += "[general time zone]"; break; case "Z": resultStr += "[rfc 822 time zone]"; break; case "'": if (patternStr.substr(1,1) == "'") { resultStr += "'"; subPatternLength = 2; } else { var txt = patternStr.match(/^'([^']|'')*'/g)[0]; subPatternLength = txt.length; var strippedTxt = txt.substring(1, txt.length-1).replace(/''/g, "'"); resultStr += strippedTxt; } break; default: var alphaRe = new RegExp("[A-Za-z]", "g") if (!token.match(alphaRe)) { resultStr += token; subPatternLength = 1; } break; } patternStr = patternStr.substring(subPatternLength, patternStr.length); } return resultStr; } var dateLanguage = { monthNames : ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'], monthNamesShort : ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'], weekDayNames : ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'], weekDayNamesShort : ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'], weekDayNamesTiny : ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'], weekDayNamesAbbrev : ['S', 'M', 'T', 'W', 'T', 'F', 'S'], eraNames : ['BC', 'AD'], amPmNames : ['AM', 'PM'] }; |
The core of this routine is a simple regular expression that counts the number of subsequent occurrences of the first token in the string. Once we have the token and its length, we add the correctly formatted date string to the result, trim the used token, and go on to the next one.
There are a few items not yet implemented. The Java date tokens w (week in year), W (week in month), D (day in year), and F (day of week in month) weren’t necessary for the project, nor were the two time zone tokens, z and Z, because we were recording and redisplaying unadjusted dates and times reported by the user, making time zone immaterial.
