resources/src/jquery/jquery.byteLimit.js

   1 /**
   2  * @class jQuery.plugin.byteLimit
   3  */
   4 ( function ( $, mw ) {
   5
   6         var
   7                 eventKeys = [
   8                         'keyup.byteLimit',
   9                         'keydown.byteLimit',
  10                         'change.byteLimit',
  11                         'mouseup.byteLimit',
  12                         'cut.byteLimit',
  13                         'paste.byteLimit',
  14                         'focus.byteLimit',
  15                         'blur.byteLimit'
  16                 ].join( ' ' ),
  17                 trimByteLength = require( 'mediawiki.String' ).trimByteLength;
  18
  19         /**
  20          * Utility function to trim down a string, based on byteLimit
  21          * and given a safe start position. It supports insertion anywhere
  22          * in the string, so "foo" to "fobaro" if limit is 4 will result in
  23          * "fobo", not "foba". Basically emulating the native maxlength by
  24          * reconstructing where the insertion occurred.
  25          *
  26          * @method trimByteLength
  27          * @deprecated Use `require( 'mediawiki.String' ).trimByteLength` instead.
  28          * @static
  29          * @param {string} safeVal Known value that was previously returned by this
  30          * function, if none, pass empty string.
  31          * @param {string} newVal New value that may have to be trimmed down.
  32          * @param {number} byteLimit Number of bytes the value may be in size.
  33          * @param {Function} [fn] See jQuery#byteLimit.
  34          * @return {Object}
  35          * @return {string} return.newVal
  36          * @return {boolean} return.trimmed
  37          */
  38         mw.log.deprecate( $, 'trimByteLength', trimByteLength,
  39                 'Use require( \'mediawiki.String\' ).trimByteLength instead.', '$.trimByteLength' );
  40
  41         /**
  42          * Enforces a byte limit on an input field, so that UTF-8 entries are counted as well,
  43          * when, for example, a database field has a byte limit rather than a character limit.
  44          * Plugin rationale: Browser has native maxlength for number of characters, this plugin
  45          * exists to limit number of bytes instead.
  46          *
  47          * Can be called with a custom limit (to use that limit instead of the maxlength attribute
  48          * value), a filter function (in case the limit should apply to something other than the
  49          * exact input value), or both. Order of parameters is important!
  50          *
  51          * @param {number} [limit] Limit to enforce, fallsback to maxLength-attribute,
  52          *  called with fetched value as argument.
  53          * @param {Function} [fn] Function to call on the string before assessing the length.
  54          * @return {jQuery}
  55          * @chainable
  56          */
  57         $.fn.byteLimit = function ( limit, fn ) {
  58                 // If the first argument is the function,
  59                 // set fn to the first argument's value and ignore the second argument.
  60                 if ( $.isFunction( limit ) ) {
  61                         fn = limit;
  62                         limit = undefined;
  63                 // Either way, verify it is a function so we don't have to call
  64                 // isFunction again after this.
  65                 } else if ( !fn || !$.isFunction( fn ) ) {
  66                         fn = undefined;
  67                 }
  68
  69                 // The following is specific to each element in the collection.
  70                 return this.each( function ( i, el ) {
  71                         var $el, elLimit, prevSafeVal;
  72
  73                         $el = $( el );
  74
  75                         // If no limit was passed to byteLimit(), use the maxlength value.
  76                         // Can't re-use 'limit' variable because it's in the higher scope
  77                         // that would affect the next each() iteration as well.
  78                         // Note that we use attribute to read the value instead of property,
  79                         // because in Chrome the maxLength property by default returns the
  80                         // highest supported value (no indication that it is being enforced
  81                         // by choice). We don't want to bind all of this for some ridiculously
  82                         // high default number, unless it was explicitly set in the HTML.
  83                         // Also cast to a (primitive) number (most commonly because the maxlength
  84                         // attribute contains a string, but theoretically the limit parameter
  85                         // could be something else as well).
  86                         elLimit = Number( limit === undefined ? $el.attr( 'maxlength' ) : limit );
  87
  88                         // If there is no (valid) limit passed or found in the property,
  89                         // skip this. The < 0 check is required for Firefox, which returns
  90                         // -1  (instead of undefined) for maxLength if it is not set.
  91                         if ( !elLimit || elLimit < 0 ) {
  92                                 return;
  93                         }
  94
  95                         if ( fn ) {
  96                                 // Save function for reference
  97                                 $el.data( 'byteLimit.callback', fn );
  98                         }
  99
 100                         // Remove old event handlers (if there are any)
 101                         $el.off( '.byteLimit' );
 102
 103                         if ( fn ) {
 104                                 // Disable the native maxLength (if there is any), because it interferes
 105                                 // with the (differently calculated) byte limit.
 106                                 // Aside from being differently calculated (average chars with byteLimit
 107                                 // is lower), we also support a callback which can make it to allow longer
 108                                 // values (e.g. count "Foo" from "User:Foo").
 109                                 // maxLength is a strange property. Removing or setting the property to
 110                                 // undefined directly doesn't work. Instead, it can only be unset internally
 111                                 // by the browser when removing the associated attribute (Firefox/Chrome).
 112                                 // https://bugs.chromium.org/p/chromium/issues/detail?id=136004
 113                                 $el.removeAttr( 'maxlength' );
 114
 115                         } else {
 116                                 // If we don't have a callback the bytelimit can only be lower than the charlimit
 117                                 // (that is, there are no characters less than 1 byte in size). So lets (re-)enforce
 118                                 // the native limit for efficiency when possible (it will make the while-loop below
 119                                 // faster by there being less left to interate over).
 120                                 $el.attr( 'maxlength', elLimit );
 121                         }
 122
 123                         // Safe base value, used to determine the path between the previous state
 124                         // and the state that triggered the event handler below - and enforce the
 125                         // limit approppiately (e.g. don't chop from the end if text was inserted
 126                         // at the beginning of the string).
 127                         prevSafeVal = '';
 128
 129                         // We need to listen to after the change has already happened because we've
 130                         // learned that trying to guess the new value and canceling the event
 131                         // accordingly doesn't work because the new value is not always as simple as:
 132                         // oldValue + String.fromCharCode( e.which ); because of cut, paste, select-drag
 133                         // replacements, and custom input methods and what not.
 134                         // Even though we only trim input after it was changed (never prevent it), we do
 135                         // listen on events that input text, because there are cases where the text has
 136                         // changed while text is being entered and keyup/change will not be fired yet
 137                         // (such as holding down a single key, fires keydown, and after each keydown,
 138                         // we can trim the previous one).
 139                         // See https://www.w3.org/TR/DOM-Level-3-Events/#events-keyboard-event-order for
 140                         // the order and characteristics of the key events.
 141                         $el.on( eventKeys, function () {
 142                                 var res = trimByteLength(
 143                                         prevSafeVal,
 144                                         this.value,
 145                                         elLimit,
 146                                         fn
 147                                 );
 148
 149                                 // Only set value property if it was trimmed, because whenever the
 150                                 // value property is set, the browser needs to re-initiate the text context,
 151                                 // which moves the cursor at the end the input, moving it away from wherever it was.
 152                                 // This is a side-effect of limiting after the fact.
 153                                 if ( res.trimmed === true ) {
 154                                         this.value = res.newVal;
 155                                         // Trigger a 'change' event to let other scripts attached to this node know that the value
 156                                         // was changed. This will also call ourselves again, but that's okay, it'll be a no-op.
 157                                         $el.trigger( 'change' );
 158                                 }
 159                                 // Always adjust prevSafeVal to reflect the input value. Not doing this could cause
 160                                 // trimByteLength to compare the new value to an empty string instead of the
 161                                 // old value, resulting in trimming always from the end (T42850).
 162                                 prevSafeVal = res.newVal;
 163                         } );
 164                 } );
 165         };
 166
 167         /**
 168          * @class jQuery
 169          * @mixins jQuery.plugin.byteLimit
 170          */
 171 }( jQuery, mediaWiki ) );