Bridge para encapsular o Cross Browser

{ October 5th, 2007 }


cmilfont

Autor: cmilfont

No rastro do meu √ļltimo post, aproveitando a deixa de detec√ß√£o otimizada trabalhando junto com o Design Pattern Bridge, aproveitaremos esse conceito para encapsularmos a complexidade de se trabalhar com c√≥digos que tenham que rodar em m√ļltiplos Browsers.

O padr√£o Bridge define o desacoplamento da abstra√ß√£o (interface) com suas implementa√ß√Ķes e cada implementa√ß√£o possa variar independentemente.

No código passado vimos isso implementado na função addEvent como segue:

var addEvent = function(el, type, fn) {
    el['on'+type] = fn;
};
if(document.addEventListener) {
    addEvent = function(el, type, fn) {
        el.addEventListener(type, fn, false);
    };
} else if(document.attachEvent) {
    addEvent = function(el, type, fn) {
        el.attachEvent('on'+type, fn);
    };
}

Nesse código o método addEvent é uma forma genérica de adicionar eventos a um elemento DOM na página e encapsula o comportamento implementado pelos Browsers. Essa estratégia pode e deve ser adotada em todo o código que necessite de implementação diferente dependendo do navegador, o chamado Cross Browser.

Cross Browser √© a t√©cnica de implementar uma constru√ß√£o que rode em m√ļltiplos navegadores sem diferen√ßa percept√≠vel ao usu√°rio. O custo de aplicar essa t√©cnica √© diminuir a performance da aplica√ß√£o como um todo, aumentar a complexidade do c√≥digo mantido, propiciar um ambiente mais sujeito a falhas de implementa√ß√£o e cair em bugs do pr√≥prio navegador (como o Memory-Leak no IE).

Instanciar o objeto XMLHttpRequest é outra situação que possui diferença entre o líder de mercado e os demais navegadores. Aplicando essa técnica, faríamos o seguinte código:

var getXHR = function() {
	this.http = new XMLHttpRequest;
	return this.http;
}
var isIE = !!document.attachEvent;
if(isIE) {
      var msxml = [
        'MSXML2.XMLHTTP.3.0',
        'MSXML2.XMLHTTP',
        'Microsoft.XMLHTTP'
      ];
      for (var i=0, len = msxml.length; i < len; ++i) {
        try {
          http = new ActiveXObject(msxml[i]);
          //cria nova implementação
          getXHR = function() {
            return new ActiveXObject(msxml[i]);
          };
          break;
        }
        catch(e) {}
      }
};

Dei a dica no artigo passado de criar um arquivo para cada implementação de navegador diferente e aplicar o conceito de Lazy Loading para carregar sob demanda.

Categories: Ajax, Design Patterns, JavaScript, Melhores pr√°ticas ~ ~ Trackback


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15 Responses to “Bridge para encapsular o Cross Browser”

  1. 1
    Rafael Ponte

    Opa! Excelente post :))

    Hoje com a gama de frameworks/APIs javascripts a preocupa√ß√£o com cross-browser recai bem menos aos desenvolvedores, sorte nossa! Contudo, ainda h√° v√°rias “gambis” que somos for√ßados a implementar para que funcione em diveros browsers, rss

  2. 2
    Handerson Frota

    Hum, mas será que seria interessante essa implementação para sistemas mais complexos ?

    Mas parabêns gostei da ideia sim.

  3. 3
    cmilfont

    Sim, construir fun√ß√Ķes que encapsulem a diferen√ßa dos browsers √© at√© melhor para sistemas mais complexos, que precisam fazer essas chamadas o tempo todo e a todo momento voce ter que verificar qual o browser.

  4. 4
    Rafael via Rec6

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