[jquery] How to enable CORS in flask

All the responses above work okay, but you'll still probably get a CORS error, if the application throws an error you are not handling, like a key-error, if you aren't doing input validation properly, for example. You could add an error handler to catch all instances of exceptions and add CORS response headers in the server response

So define an error handler - errors.py:

from flask import json, make_response, jsonify
from werkzeug.exceptions import HTTPException

# define an error handling function
def init_handler(app):

    # catch every type of exception
    @app.errorhandler(Exception)
    def handle_exception(e):

        #loggit()!          

        # return json response of error
        if isinstance(e, HTTPException):
            response = e.get_response()
            # replace the body with JSON
            response.data = json.dumps({
                "code": e.code,
                "name": e.name,
                "description": e.description,
            })
        else:
            # build response
            response = make_response(jsonify({"message": 'Something went wrong'}), 500)

        # add the CORS header
        response.headers['Access-Control-Allow-Origin'] = '*'
        response.content_type = "application/json"
        return response

then using Billal's answer:

from flask import Flask
from flask_cors import CORS

# import error handling file from where you have defined it
from . import errors

app = Flask(__name__)
CORS(app) # This will enable CORS for all routes
errors.init_handler(app) # initialise error handling 

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