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請問第二高票的改變背景的兩行代碼是什么意思？如何實現(xiàn)的，麻煩詳細解答下，謝謝

var?str_tr=document.getElementsByTagName('tr');
??????????for(var?i=0;i<str_tr.length;i++){
???????????str_tr[i].setAttribute('onmouseover',document.all???eval(function(){this.style.background="#f2f2f2"})?:?'javascript:this.style.background="#f2f2f2"');
???????????str_tr[i].setAttribute('onmouseout',document.all?eval(function(){this.style.background="#fff"}):'javascript:this.style.background="#fff"');
???????}

weibo_Gingbery_0

2017-01-03

源自：JavaScript進階篇 9-22

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EastEgg
2017-01-03

var?str_tr=document.getElementsByTagName('tr'); ?//獲取文檔中的tr元素并儲存到變量str_tr中

??????????for(var?i=0;i<str_tr.length;i++){ ?//循環(huán)遍歷str_tr中的tr

???????????str_tr[i].setAttribute('onmouseover',document.all???eval(function(){this.style.background="#f2f2f2"})?:?'javascript:this.style.background="#f2f2f2"'); ?//給str_tr中的tr設置onmouseover屬性，并三元運算判斷。應該是為了兼容的需要吧。

???????????str_tr[i].setAttribute('onmouseout',document.all?eval(function(){this.style.background="#fff"}):'javascript:this.style.background="#fff"');

???????}