JavaScript向Flask传参异常：除title外参数为None的问题

Hey there! Let's break down why your category and content parameters are showing up as None in Flask, and how to fix this issue quickly.

问题根源：HTML实体编码的干扰 #

Looking at your request log, the key clue is the & strings instead of plain & between parameters:

127.0.0.1 - - [09/Aug/2020 21:53:09] "GET /modify?title=2+입니다&content=2고요&category=데이터 HTTP/1.1" 200 -

This happens because Jinja2 (Flask's templating engine) automatically escapes HTML special characters by default to prevent cross-site scripting (XSS) attacks. The & character in the URL generated by url_for gets converted to the HTML entity &—which is safe for HTML contexts, but breaks URL parameter parsing.

When the browser sends this request, Flask interprets the parameters like this:

• title=2+입니다 (this works fine)
• amp;content=2고요 (it looks for a parameter named amp;content, not content)
• amp;category=데이터 (same issue—looking for amp;category instead of category)

Since those misnamed parameters don't exist, request.args.get() returns None for category and content.

解决方案：用safe过滤器禁用转义 #

To fix this, you need to tell Jinja2 not to escape the output of url_for when using it in a JavaScript context. Just add the |safe filter to your url_for call in the script:

function popupForModifying() {
 let option = "width=820, height=400, toolbar=no, menubar=no, location=no, directories=no, status=no, scrollbars=yes, resizable=no";
 window.open("{{ url_for('modify', content=content[2], title=content[0], category=content[4])|safe }}", "", option);
}

The safe filter marks the generated URL string as "safe" for rendering without escaping, so the & characters will stay as & instead of being converted to &.

验证修改效果 #

After making this change, your request log should show a clean URL with regular & separators:

127.0.0.1 - - [DD/Mon/YYYY HH:MM:SS] "GET /modify?title=2+입니다&content=2고요&category=데이터 HTTP/1.1" 200 -

Now Flask's request.args.get('category') and request.args.get('content') will correctly retrieve the values you passed from the template.

内容的提问来源于stack exchange，提问作者Suhyeon CHOI