error: SyntaxError: Unexpected token B in JSON at position 0

问题

I am trying to set up a user register form using react and then sending the inputs to the express backend api to register the new user. I keep gettting the error: Register.js:19 POST http://localhost:3000/api/register 400 (Bad Request) and: error: SyntaxError: Unexpected token B in JSON at position 0 on the client side. On the server side I try and console.log(req.body) and only an empty object gets returned.

My react register code

import React from 'react'

class Register extends React.Component {
    state = {
        name: "",
        username: "",
        password: ""
    }

    handleChange = event => {
        const { name, value } = event.target
        this.setState({[name]:value})
    }

    handleSubmit = event => {
        event.preventDefault();
       

        fetch("/api/register", {
            method: "POST",
            body: JSON.stringify(this.state),
            headers: {
                'Content-Type': 'application/json'
            }
        }).then(res => res.json())
        .then(response => console.log("success:", JSON.stringify(response)))
        .catch(error => console.log("error:", error));
    }
    
    render() {
        return (
            <div>
                <form onSubmit={this.handleSubmit}>
                    <input type="text" name="name" value={this.state.name} placeholder="name" onChange={this.handleChange} />
                    <input type="text" name="username" value={this.state.username} placeholder="username" onChange={this.handleChange} />
                    <input type="password" name="password" value={this.state.password} placeholder="password" onChange={this.handleChange} />
                    <button>Register</button>
                </form>
            </div>
        )
    }
}

export default Register

Server side code

const express = require("express"),
      passport = require("passport"),
      User = require("../models/user");

const router = express.Router({mergeParams: true});


// /api before this
router.post("/register", (req, res)=>{
    console.log(req.body);
    const newUser = new User({
        username: req.body.username,
        name: req.body.name
    });
    User.register(newUser, req.body.password, (err, user)=>{
        if(err) {
            console.log(err);
        }
        passport.authenticate("local")(req, res, ()=>{
            res.json(user);
        });
    });
});

module.exports = router;

来源：https://stackoverflow.com/questions/59364193/error-syntaxerror-unexpected-token-b-in-json-at-position-0

标签

node.js

reactjs

express