I read this article at https://healeycodes.com/talking-between-languages about passing data between Python and JavaScript. I don’t understand the purpose of returning “OK”, 200.

I understand that “OK” is parsed to JavaScript and also logged in the console at the end of the index.js file ,but I don’t know what the 200 does.

# app.py
from flask import Flask, jsonify, request, render_template
app = Flask(__name__)

@app.route('/hello', methods=['GET', 'POST'])
def hello():

    # POST request
    if request.method == 'POST':
        print('Incoming..')
        print(request.get_json())  # parse as JSON
        return 'OK', 200 <---------------------------------------------------------------

    # GET request
    else:
        message = {'greeting':'Hello from Flask!'}
        return jsonify(message)  # serialize and use JSON headers

@app.route('/test')
def test_page():
    # look inside `templates` and serve `index.html`
    return render_template('index.html')

//index.js
// GET is the default method, so we don't need to set it
fetch('/hello')
    .then(function (response) {
        return response.text();
    }).then(function (text) {
        console.log('GET response text:');
        console.log(text); // Print the greeting as text
    });

// Send the same request
fetch('/hello')
    .then(function (response) {
        return response.json(); // But parse it as JSON this time
    })
    .then(function (json) {
        console.log('GET response as JSON:');
        console.log(json); // Here’s our JSON object
    })
// POST
fetch('/hello', {

    // Declare what type of data we're sending
    headers: {
      'Content-Type': 'application/json'
    },

    // Specify the method
    method: 'POST',

    // A JSON payload
    body: JSON.stringify({
        "greeting": "Hello from the browser!"
    })
}).then(function (response) { // At this point, Flask has printed our JSON
    return response.text();
}).then(function (text) {

    console.log('POST response: ');

    // Should be 'OK' if everything was successful
    console.log(text);
});