Fossil

  let payload = opt.payload, jsonResponse = false;
  if(payload){
    opt.method = 'POST';
    if(!(payload instanceof FormData)
       && !(payload instanceof Document)
       && !(payload instanceof Blob)
       && !(payload instanceof File)
       && !(payload instanceof ArrayBuffer)){
      if('object'===typeof payload || payload instanceof Array){
        payload = JSON.stringify(payload);
        opt.contentType = 'application/json';
       && !(payload instanceof ArrayBuffer)
       && ('object'===typeof payload
           || payload instanceof Array)){
      payload = JSON.stringify(payload);
      opt.contentType = 'application/json';
      }
    }
  }
  const url=[window.fossil.repoUrl(uri,opt.urlParams)],
        x=new XMLHttpRequest();
  if('POST'===opt.method && 'string'===typeof opt.contentType){
    x.setRequestHeader('Content-Type',opt.contentType);
  }