text: var data = JSON.stringify({
    number: 1,
    string: 'f"oo',
    arr: [1, 2, 3],
    nested: {
      a: 'b',
    },
    arr_mix: [
      1,
      'a',
      {
        arr_mix_nested: {},
      },
    ],
    boolean: false,
  });
  
  var xhr = new XMLHttpRequest();
  xhr.withCredentials = true;
  
  xhr.addEventListener('readystatechange', function() {
    if (this.readyState === this.DONE) {
      console.log(this.responseText);
    }
  });
  
  xhr.open('POST', 'http://mockbin.com/har');
  xhr.setRequestHeader('content-type', 'application/json');
  
  xhr.send(data);
  