Understanding HTTP Request Parameter Formats and Content-Type

Background

When an interface cannot be called, developers often wonder whether the problem lies in the parameter type they passed. The two most common difficulties in front‑back integration are incorrect parameter format and cross‑origin issues.

This article focuses on the first problem: what kinds of parameter formats exist and how to use them.

Thinking

For a POST request, who determines the request parameter type? Two possible answers are presented: (1) the backend interface restricts the accepted data type, or (2) the frontend decides the request parameter type when sending the request.

1. HTTP request parameter issue

The HTTP message consists of the request line, headers, and the body. This article concentrates on the data format inside the request body.

2. Various request parameter forms

1) GET request URL parameters (Query String Parameters)

Parameters are appended to the URL after a “?” and are URL‑encoded.

When using this method, developers usually serialize the object parameters before sending the request. For example, an Axios GET request can place parameters directly in the URL.

2) POST request common encoding types

First: application/json

This Content‑Type tells the server that the request body contains a JSON string, which is convenient for sending complex structured data.

Second: application/x-www-form-urlencoded

This is the classic URL‑encoded form submission where key‑value pairs are encoded as key1=val1&key2=val2. The server can parse this format easily.

Example payload:

Third: multipart/form-data

Used for file uploads. The request body is split into multiple parts, each with its own Content‑Disposition header.

Demo request using FormData:

Fourth: text/xml

This Content‑Type is used when the payload is XML, often in SOAP‑like remote calls.

Answer

The root cause of the parameter problem is usually the Content‑Type header. The frontend decides the request parameter data type, but the backend must be able to parse it correctly.

If the backend reports a parameter format error, consider which Content‑Type is appropriate for the current scenario.

How to define different types of parameters?

Third‑party tools such as qs can serialize parameters. Native JavaScript utilities like new FormData() or URLSearchParams can also be used.

Example JavaScript object and its URL‑encoded representation:

const params = {
  name: 'John Doe',
  age: 30,
  city: 'New York'
};

After processing with URLSearchParams, it becomes: name=John%20Doe&age=30&city=New%20York Why does Content‑Type exist?

Different Content‑Types correspond to different encoding schemes. Specifying the charset ensures browsers render characters correctly, preventing issues with special symbols and guaranteeing consistent interpretation across platforms.