file.js

// fetch()

const url = 'http://localhost/test.htm';
const options = {
  method: 'POST',
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/json;charset=UTF-8'
  },
  body: JSON.stringify({
    a: 10,
    b: 20
  })
};

fetch(url, options)
  .then(response => {
    console.log(response.status);
  });