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jquery.lengthLimit.js
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jquery.lengthLimit.js
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/**
* Limit string length.
*
* This module provides {@link jQuery} plugins that place different types of limits on strings.
* To use the plugins, load the module with {@link mw.loader}.
*
* For other methods for managing strings, see {@link module:mediawiki.String}.
*
* @example
* mw.loader.using( 'jquery.lengthLimit' ).then( () => {
* // Create an input that only accepts values <= 4 bytes. For example: 💪💪 is not a permitted value.
* $( '<input type="text" value="💪">' ).byteLimit( 4 ).appendTo(document.body);
* } );
*
* @module jquery.lengthLimit
*/
( function () {
const
eventKeys = [
'keyup.lengthLimit',
'keydown.lengthLimit',
'change.lengthLimit',
'mouseup.lengthLimit',
'cut.lengthLimit',
'paste.lengthLimit',
'focus.lengthLimit',
'blur.lengthLimit'
].join( ' ' ),
trimByteLength = require( 'mediawiki.String' ).trimByteLength,
trimCodePointLength = require( 'mediawiki.String' ).trimCodePointLength;
/**
* Utility function to trim down a string, based on byteLimit
* and given a safe start position.
*
* It supports insertion anywhere in the string, so "foo" to "fobaro" if
* limit is 4 will result in "fobo", not "foba". Basically emulating the
* native maxlength by reconstructing where the insertion occurred.
*
* @method '$.fn.trimByteLength'
* @memberof module:jquery.lengthLimit
* @deprecated Use {@link module:mediawiki.String.trimByteLength require( 'mediawiki.String' ).trimByteLength}
* instead.
* @static
* @param {string} safeVal Known value that was previously returned by this
* function, if none, pass empty string.
* @param {string} newVal New value that may have to be trimmed down.
* @param {number} byteLimit Number of bytes the value may be in size.
* @param {Function} [filterFunction] See jQuery#byteLimit.
* @return {module:mediawiki.String~StringTrimmed}
*/
mw.log.deprecate( $, 'trimByteLength', trimByteLength,
'Use require( \'mediawiki.String\' ).trimByteLength instead.', '$.trimByteLength' );
function lengthLimit( trimFn, limit, filterFunction ) {
const allowNativeMaxlength = trimFn === trimByteLength;
// If the first argument is the function,
// set filterFunction to the first argument's value and ignore the second argument.
if ( typeof limit === 'function' ) {
filterFunction = limit;
limit = undefined;
// Either way, verify it is a function so we don't have to call
// isFunction again after this.
} else if ( !filterFunction || typeof filterFunction !== 'function' ) {
filterFunction = undefined;
}
// The following is specific to each element in the collection.
return this.each( ( i, el ) => {
const $el = $( el );
// If no limit was passed to lengthLimit(), use the maxlength value.
// Can't re-use 'limit' variable because it's in the higher scope
// that would affect the next each() iteration as well.
// Note that we use attribute to read the value instead of property,
// because in Chrome the maxLength property by default returns the
// highest supported value (no indication that it is being enforced
// by choice). We don't want to bind all of this for some ridiculously
// high default number, unless it was explicitly set in the HTML.
// Also cast to a (primitive) number (most commonly because the maxlength
// attribute contains a string, but theoretically the limit parameter
// could be something else as well).
const elLimit = Number( limit === undefined ? $el.attr( 'maxlength' ) : limit );
// If there is no (valid) limit passed or found in the property,
// skip this. The < 0 check is required for Firefox, which returns
// -1 (instead of undefined) for maxLength if it is not set.
if ( !elLimit || elLimit < 0 ) {
return;
}
if ( filterFunction ) {
// Save function for reference
$el.data( 'lengthLimit.callback', filterFunction );
}
// Remove old event handlers (if there are any)
$el.off( '.lengthLimit' );
if ( filterFunction || !allowNativeMaxlength ) {
// Disable the native maxLength (if there is any), because it interferes
// with the (differently calculated) character/byte limit.
// Aside from being differently calculated,
// we also support a callback which can make it to allow longer
// values (e.g. count "Foo" from "User:Foo").
// maxLength is a strange property. Removing or setting the property to
// undefined directly doesn't work. Instead, it can only be unset internally
// by the browser when removing the associated attribute (Firefox/Chrome).
// https://bugs.chromium.org/p/chromium/issues/detail?id=136004
$el.removeAttr( 'maxlength' );
} else {
// For $.byteLimit only, if we don't have a callback,
// the byteLimit can only be lower than the native maxLength limit
// (that is, there are no characters less than 1 byte in size). So lets (re-)enforce
// the native limit for efficiency when possible (it will make the while-loop below
// faster by there being less left to interate over). This does not work for $.codePointLimit
// (code units for surrogates represent half a character each).
$el.attr( 'maxlength', elLimit );
}
// Safe base value, used to determine the path between the previous state
// and the state that triggered the event handler below - and enforce the
// limit approppiately (e.g. don't chop from the end if text was inserted
// at the beginning of the string).
let prevSafeVal = '';
// We need to listen to after the change has already happened because we've
// learned that trying to guess the new value and canceling the event
// accordingly doesn't work because the new value is not always as simple as:
// oldValue + String.fromCharCode( e.which ); because of cut, paste, select-drag
// replacements, and custom input methods and what not.
// Even though we only trim input after it was changed (never prevent it), we do
// listen on events that input text, because there are cases where the text has
// changed while text is being entered and keyup/change will not be fired yet
// (such as holding down a single key, fires keydown, and after each keydown,
// we can trim the previous one).
// See https://www.w3.org/TR/DOM-Level-3-Events/#events-keyboard-event-order for
// the order and characteristics of the key events.
function enforceLimit() {
const res = trimFn(
prevSafeVal,
this.value,
elLimit,
filterFunction
);
// Only set value property if it was trimmed, because whenever the
// value property is set, the browser needs to re-initiate the text context,
// which moves the cursor at the end the input, moving it away from wherever it was.
// This is a side-effect of limiting after the fact.
if ( res.trimmed === true ) {
this.value = res.newVal;
// Trigger a 'change' event to let other scripts attached to this node know that the value
// was changed. This will also call ourselves again, but that's okay, it'll be a no-op.
$el.trigger( 'change' );
}
// Always adjust prevSafeVal to reflect the input value. Not doing this could cause
// trimFn to compare the new value to an empty string instead of the
// old value, resulting in trimming always from the end (T42850).
prevSafeVal = res.newVal;
}
$el.on( eventKeys, function ( e ) {
if ( e.type === 'cut' || e.type === 'paste' ) {
// For 'cut'/'paste', the input value is only updated after the event handlers resolve.
setTimeout( enforceLimit.bind( this ) );
} else {
enforceLimit.call( this );
}
} );
} );
}
/**
* Enforces a byte limit on an input field, assuming UTF-8 encoding, for situations
* when, for example, a database field has a byte limit rather than a character limit.
* Plugin rationale: Browser has native maxlength for number of characters (technically,
* UTF-16 code units), this plugin exists to limit number of bytes instead.
*
* Can be called with a custom limit (to use that limit instead of the maxlength attribute
* value), a filter function (in case the limit should apply to something other than the
* exact input value), or both. Order of parameters is important!
*
* @memberof module:jquery.lengthLimit
* @param {number} [limit] Limit to enforce, fallsback to maxLength-attribute,
* called with fetched value as argument.
* @param {Function} [filterFunction] Function to call on the string before assessing the length.
* @return {jQuery}
* @chainable
*/
$.fn.byteLimit = function ( limit, filterFunction ) {
return lengthLimit.call( this, trimByteLength, limit, filterFunction );
};
/**
* Enforces a codepoint (character) limit on an input field.
*
* For unfortunate historical reasons, browsers' native maxlength counts [the number of UTF-16
* code units rather than Unicode codepoints][1], which means that codepoints outside the Basic
* Multilingual Plane (such as many emojis) count as 2 characters each. This plugin exists to
* correct this.
*
* [1]: https://www.w3.org/TR/html5/sec-forms.html#limiting-user-input-length-the-maxlength-attribute
*
* Can be called with a custom limit (to use that limit instead of the maxlength attribute
* value), a filter function (in case the limit should apply to something other than the
* exact input value), or both. Order of parameters is important!
*
* @memberof module:jquery.lengthLimit
* @param {number} [limit] Limit to enforce, fallsback to maxLength-attribute,
* called with fetched value as argument.
* @param {Function} [filterFunction] Function to call on the string before assessing the length.
* @return {jQuery}
* @chainable
*/
$.fn.codePointLimit = function ( limit, filterFunction ) {
return lengthLimit.call( this, trimCodePointLength, limit, filterFunction );
};
}() );

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