Question

如果我尝试通过脚本（getElementById）影响HTML元素，则仅当脚本位于该元素之后时才起作用。 javascript代码通常不是全部都放在HTML文档的顶部吗？例如：

为什么这样做：

[/usr/local/lib/python3.6/site-packages]# cd /usr/local/lib64/python3.6/site-packages/sqlalchemy/
root@ip-1-2-3-4
[/usr/local/lib64/python3.6/site-packages/sqlalchemy]# ll
total 320
drwxr-xr-x  3 root root  4096 Aug 13 17:17 connectors
-rwxr-xr-x  1 root root 40456 Aug 13 17:17 cprocessors.cpython-36m-x86_64-linux-gnu.so
-rwxr-xr-x  1 root root 51408 Aug 13 17:17 cresultproxy.cpython-36m-x86_64-linux-gnu.so
-rwxr-xr-x  1 root root 21944 Aug 13 17:17 cutils.cpython-36m-x86_64-linux-gnu.so
drwxr-xr-x  3 root root  4096 Aug 13 17:17 databases
drwxr-xr-x 10 root root  4096 Aug 13 17:17 dialects
drwxr-xr-x  3 root root  4096 Aug 13 17:17 engine
drwxr-xr-x  3 root root  4096 Aug 13 17:17 event
-rwxr-xr-x  1 root root 49746 Mar  6 14:01 events.py
-rwxr-xr-x  1 root root 12030 Mar  6 14:01 exc.py
drwxr-xr-x  4 root root  4096 Aug 13 17:17 ext
-rwxr-xr-x  1 root root  2249 Mar  6 14:01 __init__.py
-rwxr-xr-x  1 root root  3093 Mar  6 14:01 inspection.py
-rwxr-xr-x  1 root root 10967 Mar  6 14:01 interfaces.py
-rwxr-xr-x  1 root root  6712 Mar  6 14:01 log.py
drwxr-xr-x  3 root root  4096 Aug 13 17:17 orm
-rwxr-xr-x  1 root root 49883 Mar  6 14:01 pool.py
-rwxr-xr-x  1 root root  5217 Mar  6 14:01 processors.py
drwxr-xr-x  2 root root  4096 Aug 13 17:17 __pycache__
-rwxr-xr-x  1 root root  1200 Mar  6 14:01 schema.py
drwxr-xr-x  3 root root  4096 Aug 13 17:17 sql
drwxr-xr-x  5 root root  4096 Aug 13 17:17 testing
-rwxr-xr-x  1 root root  1713 Mar  6 14:01 types.py
drwxr-xr-x  3 root root  4096 Aug 13 17:17 util
root@ip-1-2-3-4
[/usr/local/lib64/python3.6/site-packages/sqlalchemy]# pwd
/usr/local/lib64/python3.6/site-packages/sqlalchemy
root@ip-1-2-3-4
[/usr/local/lib64/python3.6/site-packages/sqlalchemy]# cd /usr/local/lib/python3.6/site-packages/sqlalchemy/
bash: cd: /usr/local/lib/python3.6/site-packages/sqlalchemy/: No such file or directory

但这不是

<!DOCTYPE html>
<html>
<body>
<p id="helloMessage"> </p>
<script>
document.getElementById("helloMessage").innerHTML = "Hello, World!";
</script>
</body>
</html>

Answer 1

如果该片段非常特定，则该片段document.getElementById("helloMessage")将尝试从id为helloMessage的DOM中查找一个元素，因为该元素不存在工作

您仍然可以通过将代码放在window.onload

中来将其放在html之前。

<html>

<body>
  <script>
    window.onload = function() {
      document.getElementById("helloMessage").innerHTML = "Hello, World!";
    }
  </script>
  <p id="helloMessage"> </p>
</body>

</html>

Javascript不会影响HTML元素，除非在它下面

1 个答案: