saveBlobAsFile.js

// Specifically, as data url

var saveBlobAsFile = function(fileName, fileContents) {
  if (typeof(Blob) != 'undefined') { // using Blob
    var textFileAsBlob = new Blob([fileContents], {
      type: 'text/plain'
    });
    var downloadLink = document.createElement("a");
    downloadLink.download = fileName;
    if (window.webkitURL != null) {
      downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob);
    } else {
      downloadLink.href = window.URL.createObjectURL(textFileAsBlob);
      downloadLink.onclick = document.body.removeChild(event.target);
      downloadLink.style.display = "none";
      document.body.appendChild(downloadLink);
    }
    downloadLink.click();
  } else {
    var pp = document.createElement('a');
    pp.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(fileContents));
    pp.setAttribute('download', fileName);
    pp.onclick = document.body.removeChild(event.target);
    pp.click();
  }
} //saveBlobAsFile

var jsonObject = {
  "name": "John",
  "age": 31,
  "city": "New York"
};
var fileContents = JSON.stringify(jsonObject, null, 2);
var fileName = "data.json";

saveBlobAsFile(fileName, fileContents)