When AJAX is used, the above cross domain request error is reported (using Python flash to build the background)

Error code:

from flask import Flask,render_template
@app.route("/markdownlang/",methods=["post"])
def getMarkdownLang():
    return render_template('result.html')

Solution: add a response header on the server side to simply allow cross source.

from flask import Flask,render_template,make_response
@app.route("/markdownlang/",methods=["post"])
def getMarkdownLang():
    resp = make_response(render_template('result.html'))
    resp.headers['Access-Control-Allow-Origin'] = '*'   
    return resp

There are two other things that can go wrong:

1. the requested path is not complete. Full path http://127.0.0.1:port number/file path. Cross source must have full path. The request mode has no corresponding response code on the server side. For example, the server should have a post response for a post request