resources/jquery/jquery.byteLimit.js

   1 /**
   2  * jQuery byteLimit plugin.
   3  *
   4  * @author Jan Paul Posma, 2011
   5  * @author Timo Tijhof, 2011-2012
   6  */
   7 ( function ( $ ) {
   8
   9         /**
  10          * Utility function to trim down a string, based on byteLimit
  11          * and given a safe start position. It supports insertion anywhere
  12          * in the string, so "foo" to "fobaro" if limit is 4 will result in
  13          * "fobo", not "foba". Basically emulating the native maxlength by
  14          * reconstructing where the insertion occured.
  15          *
  16          * @param {string} safeVal Known value that was previously returned by this
  17          * function, if none, pass empty string.
  18          * @param {string} newVal New value that may have to be trimmed down.
  19          * @param {number} byteLimit Number of bytes the value may be in size.
  20          * @param {Function} fn [optional] See $.fn.byteLimit.
  21          * @return {Object} Object with:
  22          *  - {string} newVal
  23          *  - {boolean} trimmed
  24          */
  25         function trimValForByteLength( safeVal, newVal, byteLimit, fn ) {
  26                 var startMatches, endMatches, matchesLen, inpParts,
  27                         oldVal = safeVal;
  28
  29                 // Run the hook if one was provided, but only on the length
  30                 // assessment. The value itself is not to be affected by the hook.
  31                 if ( $.byteLength( fn ? fn( newVal ) : newVal ) <= byteLimit ) {
  32                         // Limit was not reached, just remember the new value
  33                         // and let the user continue.
  34                         return {
  35                                 newVal: newVal,
  36                                 trimmed: false
  37                         };
  38                 }
  39
  40                 // Current input is longer than the active limit.
  41                 // Figure out what was added and limit the addition.
  42                 startMatches = 0;
  43                 endMatches = 0;
  44
  45                 // It is important that we keep the search within the range of
  46                 // the shortest string's length.
  47                 // Imagine a user adds text that matches the end of the old value
  48                 // (e.g. "foo" -> "foofoo"). startMatches would be 3, but without
  49                 // limiting both searches to the shortest length, endMatches would
  50                 // also be 3.
  51                 matchesLen = Math.min( newVal.length, oldVal.length );
  52
  53                 // Count same characters from the left, first.
  54                 // (if "foo" -> "foofoo", assume addition was at the end).
  55                 while (
  56                         startMatches < matchesLen &&
  57                         oldVal.charAt( startMatches ) === newVal.charAt( startMatches )
  58                 ) {
  59                         startMatches += 1;
  60                 }
  61
  62                 while (
  63                         endMatches < ( matchesLen - startMatches ) &&
  64                         oldVal.charAt( oldVal.length - 1 - endMatches ) === newVal.charAt( newVal.length - 1 - endMatches )
  65                 ) {
  66                         endMatches += 1;
  67                 }
  68
  69                 inpParts = [
  70                         // Same start
  71                         newVal.substring( 0, startMatches ),
  72                         // Inserted content
  73                         newVal.substring( startMatches, newVal.length - endMatches ),
  74                         // Same end
  75                         newVal.substring( newVal.length - endMatches )
  76                 ];
  77
  78                 // Chop off characters from the end of the "inserted content" string
  79                 // until the limit is statisfied.
  80                 if ( fn ) {
  81                         while ( $.byteLength( fn( inpParts.join( '' ) ) ) > byteLimit ) {
  82                                 inpParts[1] = inpParts[1].slice( 0, -1 );
  83                         }
  84                 } else {
  85                         while ( $.byteLength( inpParts.join( '' ) ) > byteLimit ) {
  86                                 inpParts[1] = inpParts[1].slice( 0, -1 );
  87                         }
  88                 }
  89
  90                 newVal = inpParts.join( '' );
  91
  92                 return {
  93                         newVal: newVal,
  94                         trimmed: true
  95                 };
  96         }
  97
  98         var eventKeys = [
  99                 'keyup.byteLimit',
 100                 'keydown.byteLimit',
 101                 'change.byteLimit',
 102                 'mouseup.byteLimit',
 103                 'cut.byteLimit',
 104                 'paste.byteLimit',
 105                 'focus.byteLimit',
 106                 'blur.byteLimit'
 107         ].join( ' ' );
 108
 109         /**
 110          * Enforces a byte limit on an input field, so that UTF-8 entries are counted as well,
 111          * when, for example, a database field has a byte limit rather than a character limit.
 112          * Plugin rationale: Browser has native maxlength for number of characters, this plugin
 113          * exists to limit number of bytes instead.
 114          *
 115          * Can be called with a custom limit (to use that limit instead of the maxlength attribute
 116          * value), a filter function (in case the limit should apply to something other than the
 117          * exact input value), or both. Order of parameters is important!
 118          *
 119          * @context {jQuery} Instance of jQuery for one or more input elements
 120          * @param {Number} limit [optional] Limit to enforce, fallsback to maxLength-attribute,
 121          *  called with fetched value as argument.
 122          * @param {Function} fn [optional] Function to call on the string before assessing the length.
 123          * @return {jQuery} The context
 124          */
 125         $.fn.byteLimit = function ( limit, fn ) {
 126                 // If the first argument is the function,
 127                 // set fn to the first argument's value and ignore the second argument.
 128                 if ( $.isFunction( limit ) ) {
 129                         fn = limit;
 130                         limit = undefined;
 131                 // Either way, verify it is a function so we don't have to call
 132                 // isFunction again after this.
 133                 } else if ( !fn || !$.isFunction( fn ) ) {
 134                         fn = undefined;
 135                 }
 136
 137                 // The following is specific to each element in the collection.
 138                 return this.each( function ( i, el ) {
 139                         var $el, elLimit, prevSafeVal;
 140
 141                         $el = $( el );
 142
 143                         // If no limit was passed to byteLimit(), use the maxlength value.
 144                         // Can't re-use 'limit' variable because it's in the higher scope
 145                         // that would affect the next each() iteration as well.
 146                         // Note that we use attribute to read the value instead of property,
 147                         // because in Chrome the maxLength property by default returns the
 148                         // highest supported value (no indication that it is being enforced
 149                         // by choice). We don't want to bind all of this for some ridiculously
 150                         // high default number, unless it was explicitly set in the HTML.
 151                         // Also cast to a (primitive) number (most commonly because the maxlength
 152                         // attribute contains a string, but theoretically the limit parameter
 153                         // could be something else as well).
 154                         elLimit = Number( limit === undefined ? $el.attr( 'maxlength' ) : limit );
 155
 156                         // If there is no (valid) limit passed or found in the property,
 157                         // skip this. The < 0 check is required for Firefox, which returns
 158                         // -1  (instead of undefined) for maxLength if it is not set.
 159                         if ( !elLimit || elLimit < 0 ) {
 160                                 return;
 161                         }
 162
 163                         if ( fn ) {
 164                                 // Save function for reference
 165                                 $el.data( 'byteLimit.callback', fn );
 166                         }
 167
 168                         // Remove old event handlers (if there are any)
 169                         $el.off( '.byteLimit' );
 170
 171                         if ( fn ) {
 172                                 // Disable the native maxLength (if there is any), because it interferes
 173                                 // with the (differently calculated) byte limit.
 174                                 // Aside from being differently calculated (average chars with byteLimit
 175                                 // is lower), we also support a callback which can make it to allow longer
 176                                 // values (e.g. count "Foo" from "User:Foo").
 177                                 // maxLength is a strange property. Removing or setting the property to
 178                                 // undefined directly doesn't work. Instead, it can only be unset internally
 179                                 // by the browser when removing the associated attribute (Firefox/Chrome).
 180                                 // http://code.google.com/p/chromium/issues/detail?id=136004
 181                                 $el.removeAttr( 'maxlength' );
 182
 183                         } else {
 184                                 // If we don't have a callback the bytelimit can only be lower than the charlimit
 185                                 // (that is, there are no characters less than 1 byte in size). So lets (re-)enforce
 186                                 // the native limit for efficiency when possible (it will make the while-loop below
 187                                 // faster by there being less left to interate over).
 188                                 $el.attr( 'maxlength', elLimit );
 189                         }
 190
 191
 192                         // Safe base value, used to determine the path between the previous state
 193                         // and the state that triggered the event handler below - and enforce the
 194                         // limit approppiately (e.g. don't chop from the end if text was inserted
 195                         // at the beginning of the string).
 196                         prevSafeVal = '';
 197
 198                         // We need to listen to after the change has already happened because we've
 199                         // learned that trying to guess the new value and canceling the event
 200                         // accordingly doesn't work because the new value is not always as simple as:
 201                         // oldValue + String.fromCharCode( e.which ); because of cut, paste, select-drag
 202                         // replacements, and custom input methods and what not.
 203                         // Even though we only trim input after it was changed (never prevent it), we do
 204                         // listen on events that input text, because there are cases where the text has
 205                         // changed while text is being entered and keyup/change will not be fired yet
 206                         // (such as holding down a single key, fires keydown, and after each keydown,
 207                         // we can trim the previous one).
 208                         // See http://www.w3.org/TR/DOM-Level-3-Events/#events-keyboard-event-order for
 209                         // the order and characteristics of the key events.
 210                         $el.on( eventKeys, function () {
 211                                 var res = trimValForByteLength(
 212                                         prevSafeVal,
 213                                         this.value,
 214                                         elLimit,
 215                                         fn
 216                                 );
 217
 218                                 // Only set value property if it was trimmed, because whenever the
 219                                 // value property is set, the browser needs to re-initiate the text context,
 220                                 // which moves the cursor at the end the input, moving it away from wherever it was.
 221                                 // This is a side-effect of limiting after the fact.
 222                                 if ( res.trimmed === true ) {
 223                                         this.value = res.newVal;
 224                                         prevSafeVal = res.newVal;
 225                                 }
 226                         } );
 227                 } );
 228         };
 229 }( jQuery ) );