resources/src/jquery/jquery.byteLimit.js

   1 /**
   2  * @class jQuery.plugin.byteLimit
   3  */
   4 ( function ( $ ) {
   5
   6         /**
   7          * Utility function to trim down a string, based on byteLimit
   8          * and given a safe start position. It supports insertion anywhere
   9          * in the string, so "foo" to "fobaro" if limit is 4 will result in
  10          * "fobo", not "foba". Basically emulating the native maxlength by
  11          * reconstructing where the insertion occurred.
  12          *
  13          * @static
  14          * @param {string} safeVal Known value that was previously returned by this
  15          * function, if none, pass empty string.
  16          * @param {string} newVal New value that may have to be trimmed down.
  17          * @param {number} byteLimit Number of bytes the value may be in size.
  18          * @param {Function} [fn] See jQuery#byteLimit.
  19          * @return {Object}
  20          * @return {string} return.newVal
  21          * @return {boolean} return.trimmed
  22          */
  23         $.trimByteLength = function ( safeVal, newVal, byteLimit, fn ) {
  24                 var startMatches, endMatches, matchesLen, inpParts,
  25                         oldVal = safeVal;
  26
  27                 // Run the hook if one was provided, but only on the length
  28                 // assessment. The value itself is not to be affected by the hook.
  29                 if ( $.byteLength( fn ? fn( newVal ) : newVal ) <= byteLimit ) {
  30                         // Limit was not reached, just remember the new value
  31                         // and let the user continue.
  32                         return {
  33                                 newVal: newVal,
  34                                 trimmed: false
  35                         };
  36                 }
  37
  38                 // Current input is longer than the active limit.
  39                 // Figure out what was added and limit the addition.
  40                 startMatches = 0;
  41                 endMatches = 0;
  42
  43                 // It is important that we keep the search within the range of
  44                 // the shortest string's length.
  45                 // Imagine a user adds text that matches the end of the old value
  46                 // (e.g. "foo" -> "foofoo"). startMatches would be 3, but without
  47                 // limiting both searches to the shortest length, endMatches would
  48                 // also be 3.
  49                 matchesLen = Math.min( newVal.length, oldVal.length );
  50
  51                 // Count same characters from the left, first.
  52                 // (if "foo" -> "foofoo", assume addition was at the end).
  53                 while (
  54                         startMatches < matchesLen &&
  55                         oldVal.charAt( startMatches ) === newVal.charAt( startMatches )
  56                 ) {
  57                         startMatches += 1;
  58                 }
  59
  60                 while (
  61                         endMatches < ( matchesLen - startMatches ) &&
  62                         oldVal.charAt( oldVal.length - 1 - endMatches ) === newVal.charAt( newVal.length - 1 - endMatches )
  63                 ) {
  64                         endMatches += 1;
  65                 }
  66
  67                 inpParts = [
  68                         // Same start
  69                         newVal.slice( 0, startMatches ),
  70                         // Inserted content
  71                         newVal.slice( startMatches, newVal.length - endMatches ),
  72                         // Same end
  73                         newVal.slice( newVal.length - endMatches )
  74                 ];
  75
  76                 // Chop off characters from the end of the "inserted content" string
  77                 // until the limit is statisfied.
  78                 if ( fn ) {
  79                         // stop, when there is nothing to slice - bug 41450
  80                         while ( $.byteLength( fn( inpParts.join( '' ) ) ) > byteLimit && inpParts[ 1 ].length > 0 ) {
  81                                 inpParts[ 1 ] = inpParts[ 1 ].slice( 0, -1 );
  82                         }
  83                 } else {
  84                         while ( $.byteLength( inpParts.join( '' ) ) > byteLimit ) {
  85                                 inpParts[ 1 ] = inpParts[ 1 ].slice( 0, -1 );
  86                         }
  87                 }
  88
  89                 newVal = inpParts.join( '' );
  90
  91                 return {
  92                         newVal: newVal,
  93                         trimmed: true
  94                 };
  95         };
  96
  97         var eventKeys = [
  98                 'keyup.byteLimit',
  99                 'keydown.byteLimit',
 100                 'change.byteLimit',
 101                 'mouseup.byteLimit',
 102                 'cut.byteLimit',
 103                 'paste.byteLimit',
 104                 'focus.byteLimit',
 105                 'blur.byteLimit'
 106         ].join( ' ' );
 107
 108         /**
 109          * Enforces a byte limit on an input field, so that UTF-8 entries are counted as well,
 110          * when, for example, a database field has a byte limit rather than a character limit.
 111          * Plugin rationale: Browser has native maxlength for number of characters, this plugin
 112          * exists to limit number of bytes instead.
 113          *
 114          * Can be called with a custom limit (to use that limit instead of the maxlength attribute
 115          * value), a filter function (in case the limit should apply to something other than the
 116          * exact input value), or both. Order of parameters is important!
 117          *
 118          * @param {number} [limit] Limit to enforce, fallsback to maxLength-attribute,
 119          *  called with fetched value as argument.
 120          * @param {Function} [fn] Function to call on the string before assessing the length.
 121          * @return {jQuery}
 122          * @chainable
 123          */
 124         $.fn.byteLimit = function ( limit, fn ) {
 125                 // If the first argument is the function,
 126                 // set fn to the first argument's value and ignore the second argument.
 127                 if ( $.isFunction( limit ) ) {
 128                         fn = limit;
 129                         limit = undefined;
 130                 // Either way, verify it is a function so we don't have to call
 131                 // isFunction again after this.
 132                 } else if ( !fn || !$.isFunction( fn ) ) {
 133                         fn = undefined;
 134                 }
 135
 136                 // The following is specific to each element in the collection.
 137                 return this.each( function ( i, el ) {
 138                         var $el, elLimit, prevSafeVal;
 139
 140                         $el = $( el );
 141
 142                         // If no limit was passed to byteLimit(), use the maxlength value.
 143                         // Can't re-use 'limit' variable because it's in the higher scope
 144                         // that would affect the next each() iteration as well.
 145                         // Note that we use attribute to read the value instead of property,
 146                         // because in Chrome the maxLength property by default returns the
 147                         // highest supported value (no indication that it is being enforced
 148                         // by choice). We don't want to bind all of this for some ridiculously
 149                         // high default number, unless it was explicitly set in the HTML.
 150                         // Also cast to a (primitive) number (most commonly because the maxlength
 151                         // attribute contains a string, but theoretically the limit parameter
 152                         // could be something else as well).
 153                         elLimit = Number( limit === undefined ? $el.attr( 'maxlength' ) : limit );
 154
 155                         // If there is no (valid) limit passed or found in the property,
 156                         // skip this. The < 0 check is required for Firefox, which returns
 157                         // -1  (instead of undefined) for maxLength if it is not set.
 158                         if ( !elLimit || elLimit < 0 ) {
 159                                 return;
 160                         }
 161
 162                         if ( fn ) {
 163                                 // Save function for reference
 164                                 $el.data( 'byteLimit.callback', fn );
 165                         }
 166
 167                         // Remove old event handlers (if there are any)
 168                         $el.off( '.byteLimit' );
 169
 170                         if ( fn ) {
 171                                 // Disable the native maxLength (if there is any), because it interferes
 172                                 // with the (differently calculated) byte limit.
 173                                 // Aside from being differently calculated (average chars with byteLimit
 174                                 // is lower), we also support a callback which can make it to allow longer
 175                                 // values (e.g. count "Foo" from "User:Foo").
 176                                 // maxLength is a strange property. Removing or setting the property to
 177                                 // undefined directly doesn't work. Instead, it can only be unset internally
 178                                 // by the browser when removing the associated attribute (Firefox/Chrome).
 179                                 // http://code.google.com/p/chromium/issues/detail?id=136004
 180                                 $el.removeAttr( 'maxlength' );
 181
 182                         } else {
 183                                 // If we don't have a callback the bytelimit can only be lower than the charlimit
 184                                 // (that is, there are no characters less than 1 byte in size). So lets (re-)enforce
 185                                 // the native limit for efficiency when possible (it will make the while-loop below
 186                                 // faster by there being less left to interate over).
 187                                 $el.attr( 'maxlength', elLimit );
 188                         }
 189
 190                         // Safe base value, used to determine the path between the previous state
 191                         // and the state that triggered the event handler below - and enforce the
 192                         // limit approppiately (e.g. don't chop from the end if text was inserted
 193                         // at the beginning of the string).
 194                         prevSafeVal = '';
 195
 196                         // We need to listen to after the change has already happened because we've
 197                         // learned that trying to guess the new value and canceling the event
 198                         // accordingly doesn't work because the new value is not always as simple as:
 199                         // oldValue + String.fromCharCode( e.which ); because of cut, paste, select-drag
 200                         // replacements, and custom input methods and what not.
 201                         // Even though we only trim input after it was changed (never prevent it), we do
 202                         // listen on events that input text, because there are cases where the text has
 203                         // changed while text is being entered and keyup/change will not be fired yet
 204                         // (such as holding down a single key, fires keydown, and after each keydown,
 205                         // we can trim the previous one).
 206                         // See http://www.w3.org/TR/DOM-Level-3-Events/#events-keyboard-event-order for
 207                         // the order and characteristics of the key events.
 208                         $el.on( eventKeys, function () {
 209                                 var res = $.trimByteLength(
 210                                         prevSafeVal,
 211                                         this.value,
 212                                         elLimit,
 213                                         fn
 214                                 );
 215
 216                                 // Only set value property if it was trimmed, because whenever the
 217                                 // value property is set, the browser needs to re-initiate the text context,
 218                                 // which moves the cursor at the end the input, moving it away from wherever it was.
 219                                 // This is a side-effect of limiting after the fact.
 220                                 if ( res.trimmed === true ) {
 221                                         this.value = res.newVal;
 222                                 }
 223                                 // Always adjust prevSafeVal to reflect the input value. Not doing this could cause
 224                                 // trimByteLength to compare the new value to an empty string instead of the
 225                                 // old value, resulting in trimming always from the end (bug 40850).
 226                                 prevSafeVal = res.newVal;
 227                         } );
 228                 } );
 229         };
 230
 231         /**
 232          * @class jQuery
 233          * @mixins jQuery.plugin.byteLimit
 234          */
 235 }( jQuery ) );