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<code><span>if</span>(v == <span>'男'</span>) <span>{
   内容区背景变灰
   广告区内容变成男人话题
}</span><span>else</span><span>if</span>(v == <span>'女'</span>)<span>{
   内容区背景变粉
   广告区内容变成女人话题
}</span></code>

<code><span>body</span>><span>select</span><span>name</span>=<span>''</span><span>id</span>=<span>""</span>><span>option</span><span>value</span>=<span>'male'</span>>男士风格<span><span>option</span>></span><span>option</span><span>value</span>=<span>'female'</span>>女士风格<span><span>option</span>></span><span><span>select</span>></span><span>input</span><span>type</span>=<span>'button'</span><span>value</span>=<span>"观察学习区"</span><span>onclick</span>=<span>"t1();"</span>><span>input</span><span>type</span>=<span>'button'</span><span>value</span>=<span>"不再观察学习区"</span><span>onclick</span>=<span>"t2();"</span>><span>div</span><span>id</span>=<span>'content'</span>>我是内容<span><span>div</span>></span><span>div</span><span>id</span>=<span>'ad'</span>>我是广告<span><span>div</span>></span><span>div</span><span>id</span>=<span>'study'</span>>我是学习区<span><span>div</span>></span><span><span>body</span>></span></code>

<code><span>script</span>><span><span>//获取对象</span><span>var</span> sel = document.getElementsByTagName(<span>'select'</span>)[<span>0</span>];
    <span>//定义方法</span>
    sel.observers={};
    <span>//增加某个方法</span>
    sel.attach = <span><span>function</span><span>(key,obj)</span>{</span><span>this</span>.observers[key] = obj;
    }
    <span>//卸掉某个方法</span>
    sel.detach = <span><span>function</span><span>(key)</span>{</span><span>delete</span><span>this</span>.observers[key];
    }
    <span>//通知</span>
    sel.onchange = sel.notify = <span><span>function</span><span>()</span>{</span><span>for</span>(<span>var</span> key <span>in</span><span>this</span>.observers){
            <span>this</span>.observers[key].update(<span>this</span>);<span>//去调用对象的update方法</span>
        }
    }

    <span>//客户端</span><span>var</span> content = document.getElementById(<span>'content'</span>);
    <span>var</span> ad = document.getElementById(<span>'ad'</span>);
    <span>//内容区变化效果</span>
    content.update = <span><span>function</span><span>(observer)</span>{</span><span>if</span>(observer.value==<span>'male'</span>){
            <span>this</span>.style.backgroundColor=<span>'gray'</span>;
        }<span>else</span><span>if</span>(observer.value==<span>'female'</span>){
            <span>this</span>.style.backgroundColor=<span>'pink'</span>;
        }
    }
    <span>//广告区变化效果</span>
    ad.update = <span><span>function</span><span>(observer)</span>{</span><span>if</span>(observer.value==<span>'male'</span>){
            <span>this</span>.innerHTML=<span>'汽车'</span>;
        }<span>else</span><span>if</span>(observer.value==<span>'female'</span>){
            <span>this</span>.innerHTML=<span>'减肥'</span>;
        }
    }
    <span>//确定谁来监视变化</span>
    sel.attach(<span>'content'</span>,content);
    sel.attach(<span>'ad'</span>,ad);

    study = document.getElementById(<span>'study'</span>);
    sel.attach(<span>'study'</span>,study);<span>//默认为观察学习区</span>
    study.update = <span><span>function</span><span>(observer)</span>{</span><span>if</span>(observer.value==<span>'male'</span>){
            <span>this</span>.innerHTML=<span>'学习计算机'</span>;
        }<span>else</span><span>if</span>(observer.value==<span>'female'</span>){
            <span>this</span>.innerHTML=<span>'学习减肥'</span>;
        }
    }
    <span>//增加学习区的观察</span><span><span>function</span><span>t1</span><span>()</span>{</span>
        sel.attach(<span>'study'</span>,study);
    }
    <span>//取消学习区的观察</span><span><span>function</span><span>t2</span><span>()</span>{</span>
        sel.detach(<span>'study'</span>);
    }
</span><span><span>script</span>></span></code>