On the server, you don’t need a compiler-you can start using for– of in io.js (and Node, with the -harmony option) today. If you’d like to use this new syntax on the web, but you need to support IE and Safari, you can use a compiler like Babel or Google’s Traceur to translate your ES6 code to Web-friendly ES5. It also works in Microsoft’s Spartan browser, but not in shipping versions of IE. It’s supported in Chrome if you go to chrome://flags and enable “Experimental JavaScript”. The for– of loop is supported in all current Firefox releases. for– of is easy to use, but there is a lot going on behind the scenes. We could add that, but I think it would obscure what’s going on rather than illuminate it. Here is a rough equivalent, using the underlying methods and a few temporary variables: Now that we have all the details, we can take a simple for– of loop and rewrite it in terms of the underlying method calls. Most iterator objects won’t need to implement it.throw(exc) is even more of a special case: for– of never calls it at all. return() if it needs to do some cleanup or free up resources it was using. return() if the loop exits prematurely, due to an exception or a break or return statement. But all three designs are fundamentally returning the same information.Īn iterator object can also implement optional. next() method that throws StopIteration when there are no more values. value properties, is superficially different from how iterators work in other languages. ![]() ![]() Of course, a typical iterator will not be quite this trivial. How do you loop over the elements of an array? When JavaScript was introduced, twenty years ago, you would do it like this:įor (var index = 0 index < myArray.length index++) will be an infinite loop. Enable JavaScript to view data.ES6 In Depth is a series on new features being added to the JavaScript programming language in the 6th Edition of the ECMAScript standard, ES6 for short. ![]() forEach ) Especificaciones SpecificationĮCMAScript Language Specification # īCD tables only load in the browser with JavaScript enabled. Production steps of ECMA-262, Edition 5, 15.4.4.18 // Reference: if ( ! Array. El típico uso es ejecutar los efectos secundarios al final de la cadena.įoreach() no muta/modifica el array desde el que es llamado (aunque callback, si se invoca, podría hacerlo). Si los valores de los elementos existentes en el vector son modificados, el valor pasado al callback será el valor al momento de que forEach los visite no se evaluarán los elementos borrados antes de ser visitados por forEach.įorEach() ejecuta la función callback una vez por cada elemento del array a diferencia de map() o reduce() este siempre devuelve el valor undefined y no es encadenable. Los elementos que sean añadidos al vector después de que inicie la llamada a forEach no serán visitados por callback. The forEach () method calls a specified callback function once for every element it iterates over inside an array. And theres a helpful method JS devs typically use to do this: the forEach () method. Si thisArg es undefined o null, el valor this dentro de la función depende si la función está o no en modo estricto (valor pasado si está en modo estricto, objeto global si está en modo no-estricto).Įl rango de elementos procesados por forEach() se establece antes de la primera invocación del callback. In JavaScript, youll often need to iterate through an array collection and execute a callback method for each iteration. Si un parámetro thisArg es proporcionado a forEach, será usado como el valor this para cada invocación de callback como si se llamara a callback.call(thisArg, element, index, array). ![]() sobre arrays sparse)Ĭallback es invocada con tres argumentos: No es invocada para índices que han sido eliminados o que no hayan sido inicializados (Ej. ()įorEach() ejecuta la función callback una vez por cada elemento presente en el array en orden ascendente.Object.prototype._lookupSetter_() (en-US) Obsoleto.Object.prototype._lookupGetter_() (en-US) Obsoleto.Object.prototype._defineSetter_() (en-US) Obsoleto.Object.prototype._defineGetter_() Obsoleto.
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