this.http.post不会发送角度为4的参数

I need to create a login system, I try to send the params to the PHP server.

Angular app

return this.http.post<any>('/s/login/index.php', {
                username: username,
                password: password
            }).map(user => {
                console.log(username); 
                // login successful if there's a jwt token in the response
                if (user) {
                    // store user details and jwt token in local storage to keep user logged in between page refreshes
                }

                return user;
            });
    }

PHP server

if($_SERVER["REQUEST_METHOD"] == "POST"){

 // Check if username is empty
if(empty(trim($_POST["username"]))){
    $username_err = 'Please enter username.';
    $resp->body->message=$username_err;
    $resp=json_encode($resp);
    echo $resp;
}

But the server always returns

{status: "400", body: {message: "Please enter username."}}

It is because you are not setting headers.

first import necessary modules

import {HttpClient,HttpHeaders} from '@angular/common/http';
import {URLSearchParams} from '@angular/http';

try it this way.

let headers = new Headers({ 'Content-Type': 'application/x-www-form-urlencoded' });
let options = {
    headers: headers
};

let body = new URLSearchParams();
body.set('username', username);
body.set('password', password);

return this.http.post<any>('/s/login/index.php', body, options).map(user => {
            console.log(username); 
            // login successful if there's a jwt token in the response
            if (user) {
                // store user details and jwt token in local storage to keep user logged in between page refreshes
            }

            return user;
        });
}

Tell me if it does not work. I am here !