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diff --git a/files/ca/web/javascript/reference/global_objects/string/charat/index.html b/files/ca/web/javascript/reference/global_objects/string/charat/index.html new file mode 100644 index 0000000000..55a84ab7d0 --- /dev/null +++ b/files/ca/web/javascript/reference/global_objects/string/charat/index.html @@ -0,0 +1,283 @@ +--- +title: String.prototype.charAt() +slug: Web/JavaScript/Referencia/Objectes_globals/String/charAt +translation_of: Web/JavaScript/Reference/Global_Objects/String/charAt +--- +<div>{{JSRef}}</div> + +<p>El mètode <strong><code>charAt()</code></strong> retorna el caràcter especificat d'una cadena.</p> + +<h2 id="Sintaxi">Sintaxi</h2> + +<pre class="syntaxbox"><code><var>str</var>.charAt(posicio)</code></pre> + +<h3 id="Paràmetres">Paràmetres</h3> + +<dl> + <dt><code>posicio</code></dt> + <dd>Un nombre sencer entre 0 i la longitud de la cadena menys 1.</dd> +</dl> + +<h2 id="Descripció">Descripció</h2> + +<p>Els caràcters d'una cadena reben un nombre per la seva posició d'esquerra a dreta. La posició del primer caràcter és el 0 i la posició de l'últim caràcter d'una cadena anomenada <code>stringName</code> és <code>stringName.length - 1</code>. Si la <code>posicio</code> proporcionada està fora del rang vàlid JavaScript retornarà una cadena buida.</p> + +<h2 id="Exemples">Exemples</h2> + +<h3 id="Mostrar_caràcters_de_diferents_posicions_d'una_cadena">Mostrar caràcters de diferents posicions d'una cadena</h3> + +<p>L'exemple següent mostra alguns caràcters a diferents posicions de la cadena <code>"Brave new world"</code>:</p> + +<pre class="brush: js">var anyString = 'Brave new world'; + +console.log("El caràcter a la posició 0 és '" + anyString.charAt(0) + "'"); +console.log("El caràcter a la posició 1 és '" + anyString.charAt(1) + "'"); +console.log("El caràcter a la posició 2 és '" + anyString.charAt(2) + "'"); +console.log("El caràcter a la posició 3 és '" + anyString.charAt(3) + "'"); +console.log("El caràcter a la posició 4 és '" + anyString.charAt(4) + "'"); +console.log("El caràcter a la posició 999 és '" + anyString.charAt(999) + "'"); +</pre> + +<p>Les línies anteriors mostren la sortida següent:</p> + +<pre class="brush: js">El caràcter a la posició 0 és 'B' +El caràcter a la posició 1 és 'r' +El caràcter a la posició 2 és 'a' +El caràcter a la posició 3 és 'v' +El caràcter a la posició 4 és 'e' +El caràcter a la posició 999 és '' +</pre> + +<h3 id="Obtenir_caràcters_sencers">Obtenir caràcters sencers</h3> + +<p>El codi següent garanteix obtenir un caràcter sencer, fins i tot quan la cadena contingui caràcters que no formen part del pla bàsic multilingüístic.</p> + +<pre class="brush: js">var str = 'A \uD87E\uDC04 Z'; // We could also use a non-BMP character directly +for (var i = 0, chr; i < str.length; i++) { + if ((chr = getWholeChar(str, i)) === false) { + continue; + } + // Adapt this line at the top of each loop, passing in the whole string and + // the current iteration and returning a variable to represent the + // individual character + + console.log(chr); +} + +function getWholeChar(str, i) { + var code = str.charCodeAt(i); + + if (Number.isNaN(code)) { + return ''; // Position not found + } + if (code < 0xD800 || code > 0xDFFF) { + return str.charAt(i); + } + + // High surrogate (could change last hex to 0xDB7F to treat high private + // surrogates as single characters) + if (0xD800 <= code && code <= 0xDBFF) { + if (str.length <= (i + 1)) { + throw 'High surrogate without following low surrogate'; + } + var next = str.charCodeAt(i + 1); + if (0xDC00 > next || next > 0xDFFF) { + throw 'High surrogate without following low surrogate'; + } + return str.charAt(i) + str.charAt(i + 1); + } + // Low surrogate (0xDC00 <= code && code <= 0xDFFF) + if (i === 0) { + throw 'Low surrogate without preceding high surrogate'; + } + var prev = str.charCodeAt(i - 1); + + // (could change last hex to 0xDB7F to treat high private + // surrogates as single characters) + if (0xD800 > prev || prev > 0xDBFF) { + throw 'Low surrogate without preceding high surrogate'; + } + // We can pass over low surrogates now as the second component + // in a pair which we have already processed + return false; +} +</pre> + +<p>En l'entorn de l'ECMAScript 2016, que soporta assignació desestructurada, es pot utilitzar el codi següent com a versió alternativa més flexibleenvironment which allows destructured assignment, the following is a more succinct and somewhat more flexible alternative in that it does incrementing for an incrementing variable automatically (if the character warrants it in being a surrogate pair).</p> + +<pre class="brush: js">var str = 'A\uD87E\uDC04Z'; // We could also use a non-BMP character directly +for (var i = 0, chr; i < str.length; i++) { + [chr, i] = getWholeCharAndI(str, i); + // Adapt this line at the top of each loop, passing in the whole string and + // the current iteration and returning an array with the individual character + // and 'i' value (only changed if a surrogate pair) + + console.log(chr); +} + +function getWholeCharAndI(str, i) { + var code = str.charCodeAt(i); + + if (Number.isNaN(code)) { + return ''; // Position not found + } + if (code < 0xD800 || code > 0xDFFF) { + return [str.charAt(i), i]; // Normal character, keeping 'i' the same + } + + // High surrogate (could change last hex to 0xDB7F to treat high private + // surrogates as single characters) + if (0xD800 <= code && code <= 0xDBFF) { + if (str.length <= (i + 1)) { + throw 'High surrogate without following low surrogate'; + } + var next = str.charCodeAt(i + 1); + if (0xDC00 > next || next > 0xDFFF) { + throw 'High surrogate without following low surrogate'; + } + return [str.charAt(i) + str.charAt(i + 1), i + 1]; + } + // Low surrogate (0xDC00 <= code && code <= 0xDFFF) + if (i === 0) { + throw 'Low surrogate without preceding high surrogate'; + } + var prev = str.charCodeAt(i - 1); + + // (could change last hex to 0xDB7F to treat high private surrogates + // as single characters) + if (0xD800 > prev || prev > 0xDBFF) { + throw 'Low surrogate without preceding high surrogate'; + } + // Return the next character instead (and increment) + return [str.charAt(i + 1), i + 1]; +} +</pre> + +<h3 id="Fixing_charAt()_to_support_non-Basic-Multilingual-Plane_(BMP)_characters">Fixing <code>charAt()</code> to support non-Basic-Multilingual-Plane (BMP) characters</h3> + +<p>While the example above may be more frequently useful for those wishing to support non-BMP characters (since it does not require the caller to know where any non-BMP character might appear), in the event that one <em>does</em> wish, in choosing a character by index, to treat the surrogate pairs within a string as the single characters they represent, one can use the following:</p> + +<pre class="brush: js">function fixedCharAt(str, idx) { + var ret = ''; + str += ''; + var end = str.length; + + var surrogatePairs = /[\uD800-\uDBFF][\uDC00-\uDFFF]/g; + while ((surrogatePairs.exec(str)) != null) { + var li = surrogatePairs.lastIndex; + if (li - 2 < idx) { + idx++; + } else { + break; + } + } + + if (idx >= end || idx < 0) { + return ''; + } + + ret += str.charAt(idx); + + if (/[\uD800-\uDBFF]/.test(ret) && /[\uDC00-\uDFFF]/.test(str.charAt(idx + 1))) { + // Go one further, since one of the "characters" is part of a surrogate pair + ret += str.charAt(idx + 1); + } + return ret; +} +</pre> + +<h2 id="Specifications">Specifications</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">Specification</th> + <th scope="col">Status</th> + <th scope="col">Comment</th> + </tr> + <tr> + <td>{{SpecName('ES1')}}</td> + <td>{{Spec2('ES1')}}</td> + <td>Initial definition.</td> + </tr> + <tr> + <td>{{SpecName('ES5.1', '#sec-15.5.4.4', 'String.prototype.charAt')}}</td> + <td>{{Spec2('ES5.1')}}</td> + <td> </td> + </tr> + <tr> + <td>{{SpecName('ES6', '#sec-string.prototype.charat', 'String.prototype.charAt')}}</td> + <td>{{Spec2('ES6')}}</td> + <td> </td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-string.prototype.charat', 'String.prototype.charAt')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td> </td> + </tr> + </tbody> +</table> + +<h2 id="Browser_compatibility">Browser compatibility</h2> + +<div>{{CompatibilityTable}}</div> + +<div id="compat-desktop"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Chrome</th> + <th>Firefox (Gecko)</th> + <th>Internet Explorer</th> + <th>Opera</th> + <th>Safari</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + </tr> + </tbody> +</table> +</div> + +<div id="compat-mobile"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Android</th> + <th>Chrome for Android</th> + <th>Firefox Mobile (Gecko)</th> + <th>IE Mobile</th> + <th>Opera Mobile</th> + <th>Safari Mobile</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + <td>{{CompatVersionUnknown}}</td> + </tr> + </tbody> +</table> +</div> + +<h2 id="See_also">See also</h2> + +<ul> + <li>{{jsxref("String.prototype.indexOf()")}}</li> + <li>{{jsxref("String.prototype.lastIndexOf()")}}</li> + <li>{{jsxref("String.prototype.charCodeAt()")}}</li> + <li>{{jsxref("String.prototype.codePointAt()")}}</li> + <li>{{jsxref("String.prototype.split()")}}</li> + <li>{{jsxref("String.fromCodePoint()")}}</li> + <li><a href="https://mathiasbynens.be/notes/javascript-unicode">JavaScript has a Unicode problem – Mathias Bynens</a></li> +</ul> |