Unexpected token { in JSON while passing data from flask to javascript

Question

I am trying to pass simple data from flask to javascript file I am following this answer Passing a JSON object from Flask to JavaScript

But i got Uncaught SyntaxError: Unexpected token { in JSON at position 1 at JSON.parse ()

var user = JSON.parse('{{ data | tojson}}');      
 var grade=user.grade;
 console.log(grade);

my python file have code

@app.route("/quiz/0")
def quizFirst():
    data={"grade":"0"}
    return render_template('quiz.html',data=data)

the token { is not recognizable by javascript in js file, Any idea what i am missing.

is the JavaScript inside quiz.html or is it in a separate .js file? — Julien Spronck
– Julien Spronck, Commented Mar 12, 2018 at 17:52
Well this will always fail var user = JSON.parse('{{ data | tojson}}'); I don't know if maybe that's meant to get replaced somehow, but as written it will literally try to parse that string. So JSON.parse sees {{ and immediately errors. — jmcgriz
– jmcgriz, Commented Mar 12, 2018 at 17:57
so placing javascript inside is an only option, so wil i able to communicate with my js file which is seperate file? — Kharak
– Kharak, Commented Mar 12, 2018 at 18:01
Well I figured it out, any variable inside javascript in HTML file can be accessible to external(separate) js file, provided that variable is declared before its use, for that link to seperate file must be below the html javascript — Kharak
– Kharak, Commented Mar 12, 2018 at 18:21

Julien Spronck · Accepted Answer · 2018-03-12 17:59:24Z

It works for me. This JavaScript needs to be inside quiz.html. The reason is that Flask will process quiz.html and replace {{ data | tojson }} with the data provided in render_template. However, it won't process your static JS file.

quiz.html:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>sotest</title>
</head>
<body>

  Hello World!

<script>
  var user = JSON.parse('{{ data | tojson}}');      
  var grade=user.grade;
  console.log(grade);
</script>

</body>
</html>

app.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from flask import Flask, render_template
app = Flask(__name__)

@app.route("/quiz/0")
def quizFirst():
    data={"grade":"0"}
    return render_template('quiz.html',data=data)

if __name__ == "__main__":
    app.run(debug=True)

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