Download a file via javascript

Today I had an interesting challenge. I had to download a file in javascript. Why through javascript and not through a link or a form post?

• I had to set a custom accept header to get the file into a specific format (in my case in excel format)
• I had to pass too many parameters to fit in a querystring.

So here’s the code i ended up using:

export function downloadFile(url: string, message: any, method: string, contentType ? : string, acceptContentType ? : string) {
 var xhr = new XMLHttpRequest();
 xhr.open(method, url);
 if (acceptContentType) {
  xhr.setRequestHeader('Accept', acceptContentType);
 }
 if (contentType) {
  xhr.setRequestHeader('content-type', contentType);
 }
 xhr.responseType = 'blob';
 xhr.onload = function() {
  if (this.status >= 400) {
   alert('error')
  } else {
   if (window.navigator.msSaveOrOpenBlob) {
    window.navigator.msSaveOrOpenBlob(xhr.response, 'afile.xlsx');
   } else {
    var objectUrl = URL.createObjectURL(xhr.response);
    window.location.href = objectUrl;
   }
  }
 };
 xhr.send(message);
}

I tried to do this via jquery.ajax but I couldn’t get it to work. So then I switched to using xmlhttprequest. This worked fine, though saving a file in javascript works differently in chrome / explorer.