用javascript修改html元素的class

document.getElementById("collins_contentWrp").className="content-wrp dict-container closed";

document.getElementById("collins_contentWrp").setAttribute("class", "content-wrp dict-container opened");

document.getElementById("bd");

<div id="bd">

        	        <div id="ec_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#ec">基本释义</a></h4>
                                    <div id="ec" class="trans-container ec ">
                                	    <h2>
        <span>
        dog
        </span>
        <div>
                            <span>
                    英
                                            <span class="phonetic">[dɒg]</span>
                                                                <a href="#" title="真人发音" role="dict_audio_js" data-rel="http://dict.youdao.com/dictvoice?audio=dog&type=1" class="pronounce dictvoice js-ctlog"></a>
                                    </span>
                                        <span>
                     美
                                            <span class="phonetic">[dɔɡ]</span>
                                                                <a href="#" title="真人发音" role="dict_audio_js" data-rel="http://dict.youdao.com/dictvoice?audio=dog&type=2" class="pronounce dictvoice js-ctlog"></a>
                                    </span>
                                </div>
    </h2>
	        <ul>
															            			<li>n. 狗；丑女人；卑鄙的人；(俚)朋友</li>
            											            			<li>vt. 跟踪；尾随</li>
            									        </ul>

            <div class="sub">

        				        </div>
                                </div>
        </div>

        	        <div id="collins_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#collins">柯林斯英汉双解大辞典</a></h4>
                                    <div id="collins" class="trans-container collins ">
                            </div>
        </div>

        	        <div id="ec21_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#ec21">21世纪大英汉辞典</a></h4>
                                    <div id="ec21" class="trans-container ec21 ">
                            </div>
        </div>

        	        <div id="ee_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#ee">英英释义</a></h4>
                                    <div id="ee" class="trans-container ee ">
                            </div>
        </div>

        	        <div id="special_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#special">专业释义</a></h4>
                                    <div id="special" class="trans-container special ">
                            </div>
        </div>

        	        <div id="web_trans_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#web_trans">网络释义</a></h4>
                                    <div id="web_trans" class="trans-container web_trans ">
                            </div>
        </div>

        	        <div id="rel_word_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#rel_word">同根词</a></h4>
                                    <div id="rel_word" class="trans-container rel_word ">
                            </div>
        </div>

        	        <div id="syno_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#syno">同近义词</a></h4>
                                    <div id="syno" class="trans-container syno ">
                            </div>
        </div>

        	        <div id="blng_sents_part_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#blng_sents_part">双语例句</a></h4>
                                                <div id="blng_sents_part" class="trans-container blng_sents_part dict_sents_result">
                            </div>
        </div>

        	        <div id="media_sents_part_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#media_sents_part">原声例句</a></h4>
                                                <div id="media_sents_part" class="trans-container media_sents_part dict_sents_result">
                            </div>
        </div>

        	        <div id="auth_sents_part_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#auth_sents_part">权威例句</a></h4>
                                                <div id="auth_sents_part" class="trans-container auth_sents_part dict_sents_result">
                            </div>
        </div>

        	        <div id="baike_contentWrp" class="content-wrp dict-container closed">
            <h4><a class="trans-title" href="#baike">百科</a></h4>
                                    <div id="baike" class="trans-container baike ">
                            </div>
        </div>

    </div>