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mediawiki.String.js
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mediawiki.String.js
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( function () {
/**
* Calculate the byte length of a string (accounting for UTF-8).
*
* @author Jan Paul Posma, 2011
* @author Timo Tijhof, 2012
* @author David Chan, 2013
* @memberof module:mediawiki.String
* @param {string} str
* @return {number}
*/
function byteLength( str ) {
// This basically figures out how many bytes a UTF-16 string (which is what js sees)
// will take in UTF-8 by replacing a 2 byte character with 2 *'s, etc, and counting that.
// Note, surrogate (\uD800-\uDFFF) characters are counted as 2 bytes, since there's two of them
// and the actual character takes 4 bytes in UTF-8 (2*2=4). Might not work perfectly in
// edge cases such as illegal sequences, but that should never happen.
// https://en.wikipedia.org/wiki/UTF-8#Description
// The mapping from UTF-16 code units to UTF-8 bytes is as follows:
// > Range 0000-007F: codepoints that become 1 byte of UTF-8
// > Range 0080-07FF: codepoints that become 2 bytes of UTF-8
// > Range 0800-D7FF: codepoints that become 3 bytes of UTF-8
// > Range D800-DFFF: Surrogates (each pair becomes 4 bytes of UTF-8)
// > Range E000-FFFF: codepoints that become 3 bytes of UTF-8 (continued)
return str
.replace( /[\u0080-\u07FF\uD800-\uDFFF]/g, '**' )
.replace( /[\u0800-\uD7FF\uE000-\uFFFF]/g, '***' )
.length;
}
/**
* Calculate the character length of a string (accounting for UTF-16 surrogates).
*
* @memberof module:mediawiki.String
* @param {string} str
* @return {number}
*/
function codePointLength( str ) {
return str
// Low surrogate + high surrogate pairs represent one character (codepoint) each
.replace( /[\uD800-\uDBFF][\uDC00-\uDFFF]/g, '*' )
.length;
}
/**
* Like {@link https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String/charAt String.charAt()},
* but return the pair of UTF-16 surrogates for characters outside of BMP.
*
* @memberof module:mediawiki.String
* @param {string} string
* @param {number} offset Offset to extract the character
* @param {boolean} [backwards] Use backwards direction to detect UTF-16 surrogates,
* defaults to false
* @return {string}
*/
function charAt( string, offset, backwards ) {
// We don't need to check for offsets at the beginning or end of string,
// String#slice will simply return a shorter (or empty) substring.
const maybePair = backwards ?
string.slice( offset - 1, offset + 1 ) :
string.slice( offset, offset + 2 );
if ( /^[\uD800-\uDBFF][\uDC00-\uDFFF]$/.test( maybePair ) ) {
return maybePair;
} else {
return string.charAt( offset );
}
}
/**
* Lowercase the first character. Support UTF-16 surrogates for characters outside of BMP.
*
* @memberof module:mediawiki.String
* @param {string} string
* @return {string}
*/
function lcFirst( string ) {
const firstChar = charAt( string, 0 );
return firstChar.toLowerCase() + string.slice( firstChar.length );
}
/**
* Uppercase the first character. Support UTF-16 surrogates for characters outside of BMP.
*
* @memberof module:mediawiki.String
* @param {string} string
* @return {string}
*/
function ucFirst( string ) {
const firstChar = charAt( string, 0 );
return firstChar.toUpperCase() + string.slice( firstChar.length );
}
function trimLength( safeVal, newVal, length, lengthFn ) {
const oldVal = safeVal;
// Run the hook if one was provided, but only on the length
// assessment. The value itself is not to be affected by the hook.
if ( lengthFn( newVal ) <= length ) {
// Limit was not reached, just remember the new value
// and let the user continue.
return {
newVal: newVal,
trimmed: false
};
}
// Current input is longer than the active limit.
// Figure out what was added and limit the addition.
let startMatches = 0;
let endMatches = 0;
// It is important that we keep the search within the range of
// the shortest string's length.
// Imagine a user adds text that matches the end of the old value
// (e.g. "foo" -> "foofoo"). startMatches would be 3, but without
// limiting both searches to the shortest length, endMatches would
// also be 3.
const matchesLen = Math.min( newVal.length, oldVal.length );
// Count same characters from the left, first.
// (if "foo" -> "foofoo", assume addition was at the end).
while ( startMatches < matchesLen ) {
const oldChar = charAt( oldVal, startMatches, false );
const newChar = charAt( newVal, startMatches, false );
if ( oldChar !== newChar ) {
break;
}
startMatches += oldChar.length;
}
while ( endMatches < ( matchesLen - startMatches ) ) {
const oldChar = charAt( oldVal, oldVal.length - 1 - endMatches, true );
const newChar = charAt( newVal, newVal.length - 1 - endMatches, true );
if ( oldChar !== newChar ) {
break;
}
endMatches += oldChar.length;
}
const inpParts = [
// Same start
newVal.slice( 0, startMatches ),
// Inserted content
newVal.slice( startMatches, newVal.length - endMatches ),
// Same end
newVal.slice( newVal.length - endMatches )
];
// Chop off characters from the end of the "inserted content" string
// until the limit is statisfied.
// Make sure to stop when there is nothing to slice (T43450).
while ( lengthFn( inpParts.join( '' ) ) > length && inpParts[ 1 ].length > 0 ) {
// Do not chop off halves of surrogate pairs
const chopOff = /[\uD800-\uDBFF][\uDC00-\uDFFF]$/.test( inpParts[ 1 ] ) ? 2 : 1;
inpParts[ 1 ] = inpParts[ 1 ].slice( 0, -chopOff );
}
return {
newVal: inpParts.join( '' ),
// For pathological lengthFn() that always returns a length greater than the limit, we might have
// ended up not trimming - check for this case to avoid infinite loops
trimmed: newVal !== inpParts.join( '' )
};
}
/**
* @typedef {Object} module:mediawiki.String~StringTrimmed
* @property {string} newVal a trimmed version of the string
* @property {boolean} trimmed whether the string is different from the original version.
*/
/**
* 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.
*
* @memberof module:mediawiki.String
* @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] Function to call on the string before assessing the length.
* @return {module:mediawiki.String~StringTrimmed}
*/
function trimByteLength( safeVal, newVal, byteLimit, filterFunction ) {
let lengthFn;
if ( filterFunction ) {
lengthFn = function ( val ) {
return byteLength( filterFunction( val ) );
};
} else {
lengthFn = byteLength;
}
return trimLength( safeVal, newVal, byteLimit, lengthFn );
}
/**
* Utility function to trim down a string, based on codePointLimit
* 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.
*
* @memberof module:mediawiki.String
* @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} codePointLimit Number of characters the value may be in size.
* @param {Function} [filterFunction] Function to call on the string before assessing the length.
* @return {module:mediawiki.String~StringTrimmed}
*/
function trimCodePointLength( safeVal, newVal, codePointLimit, filterFunction ) {
let lengthFn;
if ( filterFunction ) {
lengthFn = function ( val ) {
return codePointLength( filterFunction( val ) );
};
} else {
lengthFn = codePointLength;
}
return trimLength( safeVal, newVal, codePointLimit, lengthFn );
}
/**
* Module providing string utility functions.
*
* @exports mediawiki.String
*/
module.exports = {
byteLength,
codePointLength,
charAt,
lcFirst,
ucFirst,
trimByteLength,
trimCodePointLength
};
}() );

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