HTTP methods are a core aspect of the Hypertext Transfer Protocol (HTTP). They specify the action that is to be performed on a given resource. Within the context of HTML forms and JavaScript, the most frequently used HTTP methods are GET and POST.

The GET method is used to retrieve data from a specified resource. When an HTML form is submitted using the GET method, the form data is appended to the URL in the form of a query string. This is visible to the user and can be bookmarked. However, due to the length limit of URLs, the GET method is not suitable for transmitting large amounts of data or sensitive information.

In contrast, the POST method is used to send data to a server to create or update a resource. Unlike the GET method, data sent via the POST method is not visible in the URL and does not have a size limit. This makes the POST method more secure and better suited for transmitting large volumes of data.

In JavaScript, these methods can be used in conjunction with the fetch API to make HTTP requests. The fetch API returns a Promise that resolves to the Response object, representing the response to the request. The method to be used is specified in the options object passed to the fetch function.

For instance, to make a GET request, you would use:

fetch('https://api.example.com/data', {
  method: 'GET',
})
  .then((response) => response.json())
  .then((data) => console.log(data));

This will fetch the data from the specified URL using the GET method, convert the response to JSON, and then log the data to the console.

For a POST request, the code would look like this:

fetch('https://api.example.com/data', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    key1: 'value1',
    key2: 'value2',
  }),
})
  .then((response) => response.json())
  .then((data) => console.log(data));

This sends a POST request to the specified URL with a JSON payload. The 'Content-Type' header is set to 'application/json', indicating that the request body contains JSON data.