Javascript 嵌套循環使瀏覽器崩潰
[英]Javascript nested loop crashes browser
問題描述
我正在使用 Django 創建一個網絡應用程序，我需要一些 Javascript 來更改動態生成元素的樣式。 我已將代碼簡化為靜態 html 和 javascript。
目標：導致問題的代碼作用於詳細信息頁面。 有許多詳細信息頁面，每個頁面都代表來自給定數據庫條目的數據。 每個頁面將有 1 個或多個表格，具體取決於數據庫條目有多少蛋白質名稱。 對於每個表，我想更改表標題中蛋白質名稱條目的顏色以及 example_id 條目的顏色。
嘗試：我正在使用 javascript 來捕獲頂級標題中的 example_id 和表標題中的蛋白質名稱。 然后我捕獲表行的節點列表並遍歷，尋找與蛋白質名稱或 example_id 匹配的條目。
問題：當迭代從嵌套循環中的表頭獲取的蛋白質名稱的節點列表時，頁面永遠不會加載。
HTML：
<html>
<body>
<h1 class="msaIdCatcher">Protein Record #example_id</h1>
<h2>Multiple Sequence Alignment</h2>
<h3 class= "msaProtNameCatcher">Protein_name1</h3>
<p>The following is a multiple sequence alignment (MSA) of all sequences predicted to be Protein_name1 sequences.</p>
<table>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id1</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>Protein_name1</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id3</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>example_id</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id4</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
</table>
<h3 class="msaProtNameCatcher">Protein_name2</h3>
<p>The following is a multiple sequence alignment (MSA) of all sequences predicted to be Protein_name2 sequences.</p>
<table>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id1</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id2</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id3</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>example_id</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>not_example_id4</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
<tr class=sequenceidrow>
<th class=sequenceid>Protein_name2</th>
<td class="alignsequence">aaaaaaaaaaaaaaaaaaaa</td>
</tr>
</table>
</body>
</html>
var idTitle = document.getElementsByClassName("msaIdCatcher");
id = idTitle[0].innerHTML;
id = id.replace("Protein Record #", "");
//Get protein_names from table headers
proteinnameElements = document.getElementsByClassName("msaProtNameCatcher")
//Get table rows
var sequenceidrowElements = document.getElementsByClassName("sequenceidrow");
//Loop through table rows
for (var i = 0; i < sequenceidrowElements.length; i++) {
//Get sequence id
var sequenceidElement = sequenceidrowElements[i].getElementsByClassName("sequenceid");
idElement = sequenceidElement[0].innerHTML
//Check if ID is ID from page heading
if (idElement == id) {
//Get sequence element and change colour of ID and sequence elemnt
var alignsequenceElement = sequenceidrowElements[i].getElementsByClassName("alignsequence");
sequenceidElement[0].style.color = "#b80090";
alignsequenceElement[0].style.color = "#b80090";
}
//Loop through protein names in table headers and Check if ID in table matches protein name
//Then change colour of ID and sequence
for (var i = 0; i < proteinnameElements.length; i++) {
proteinname = proteinnameElements[i].innerHTML
if (idElement == proteinname) {
var alignsequenceElement = sequenceidrowElements[i].getElementsByClassName("alignsequence");
sequenceidElement[0].style.color = "red";
alignsequenceElement[0].style.color = "red";
}
}
}
However, when using a single protein name by making proteinname equal to the innerHTML of the first element proteinnameElements and taking away the loop nesting as follows, the page loads in a fraction of a second.
var idTitle = document.getElementsByClassName("msaIdCatcher");
id = idTitle[0].innerHTML;
id = id.replace("Protein Record #", "");
//Get protein_names from table headers
proteinnameElements = document.getElementsByClassName("msaProtNameCatcher")
proteinname = proteinnameElements[0].innerHTML
//Get table rows
var sequenceidrowElements = document.getElementsByClassName("sequenceidrow");
//Loop through table rows
for (var i = 0; i < sequenceidrowElements.length; i++) {
//Get sequence id
var sequenceidElement = sequenceidrowElements[i].getElementsByClassName("sequenceid");
idElement = sequenceidElement[0].innerHTML
//Check if ID is ID from page heading
if (idElement == id) {
//Get sequence element and change colour of ID and sequence elemnt
var alignsequenceElement = sequenceidrowElements[i].getElementsByClassName("alignsequence");
sequenceidElement[0].style.color = "#b80090";
alignsequenceElement[0].style.color = "#b80090";
}
//Loop through protein names in table headers and Check if ID in table matches protein name
//Then change colour of ID and sequence
if (idElement == proteinname) {
var alignsequenceElement = sequenceidrowElements[i].getElementsByClassName("alignsequence");
sequenceidElement[0].style.color = "red";
alignsequenceElement[0].style.color = "red";
}
}
Can someone help me understand why nesting loops in this way causes such a large difference in runtime and help me find a way to solve my problem?
Thanks!
1 個解決方案
解決方案1
1 2020-09-11 17:51:00
你內環開始var i ，因為如何在JavaScript作用域的作品，這將是相同的i為外循環，這將是改變每次內循環運行（從而從來沒有增加外循環，使得它無窮的） ; 就像輸入這個：
var i;
for (i = 0; i < length; ++i)
{
for (i = 0; i < length2; ++i)
{
//...
}
}
要么為內循環使用不同的變量名（ j是一個常見的選擇），要么使用let關鍵字（這將確保變量是局部范圍的），這是 let 關鍵字（注意它是相對較新的）：
for (let i = 0; i < length; ++i)
{
//...
}
希望這有助於澄清事情。
JavaScript for Loop使瀏覽器崩潰
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