Pass json data via post request with fetch API and get it in express backend

Question

I'm trying to learn express and front javascript. I am trying to pass json data via post request with fetch API and want to take in on backend with express. My backend code looks like this:

const express = require('express');
const app = express();
const path = require('path');

app.get('/log', function(req, res){
    console.log("Hi");
});

app.get('/', (req, res) => res.sendFile(path.join(__dirname, 'index.html')));
app.listen(3000, () => console.log('Example app listening on port 3000!'));

and my index.html file looks like this:

<!DOCTYPE html>
<html>
<head>
<title>Fetch And Express Test</title>
</head>
<body>

    <input id="a">
    <input id="b">
    <button> Click</button>
    <script>
        document.getElementsByTagName("button")[0].addEventListener("click",function(){
            console.log("Here");
            let aInput = document.getElementById("a").value;
            let bInput = document.getElementById("b").value;

            let json = {"a": aInput, "b": bInput};
            var data = new FormData();
            data.append( "json", JSON.stringify(json));

            fetch('http://localhost:3000/log', {
                method: "POST", // *GET, POST, PUT, DELETE, etc.
                mode: "cors", // no-cors, cors, *same-origin
                cache: "no-cache", // *default, no-cache, reload, force-cache, only-if-cached
                credentials: "same-origin", // include, same-origin, *omit
                headers: {
                    "Content-Type": "application/json; charset=utf-8",
                    // "Content-Type": "application/x-www-form-urlencoded",
                },
                redirect: "follow", // manual, *follow, error
                referrer: "no-referrer", // no-referrer, *client
                body: data, // body data type must match "Content-Type" header
            })
            .then(function(res){});
        });


    </script>
</body>
</html>

Problem here is that, it doesn't log "Hi", whereas if I delete the second parameter of fetch function and only send get request, everything works fine. What's the problem?

Hodrobond · Accepted Answer · 2018-07-03 18:59:05Z

3

Your router is only set to log on a GET request, so it won't log on a POST

See here

app.get('/log', function(req, res){
    console.log("Hi");
});

app.post('/log', function(req, res){
    console.log("Hi");
});

Alternatively, you can use app.all to handle all requests.

There is a special routing method, app.all(), used to load middleware functions at a path for all HTTP request methods. For example, the following handler is executed for requests to the route “/secret” whether using GET, POST, PUT, DELETE, or any other HTTP request method supported in the http module.

app.all('/log', function (req, res, next) {
    console.log("Hi");
})

answered Jul 3, 2018 at 18:59

Hodrobond

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3 Comments

Giorgi Tsertsvadze Over a year ago

Oh, I thought get was just a function name, now it makes sense, thank you very much, after 8 mins I will be able to approve the answer.

Giorgi Tsertsvadze Over a year ago

Also can you tell me, how can I retrieve the post parameters (the json) in app.post function?

Hodrobond Over a year ago

See this question/answer

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