How do I save/export an SVG file after creating an SVG with D3.js (IE, safari and chrome)?

There are 5 steps. I often use this method to output inline svg.

1. get inline svg element to output.
2. get svg source by XMLSerializer.
3. add name spaces of svg and xlink.
4. construct url data scheme of svg by encodeURIComponent method.
5. set this url to href attribute of some "a" element, and right click this link to download svg file.

---

//get svg element.
var svg = document.getElementById("svg");

//get svg source.
var serializer = new XMLSerializer();
var source = serializer.serializeToString(svg);

//add name spaces.
if(!source.match(/^<svg[^>]+xmlns="http\:\/\/www\.w3\.org\/2000\/svg"/)){
    source = source.replace(/^<svg/, '<svg xmlns="http://www.w3.org/2000/svg"');
}
if(!source.match(/^<svg[^>]+"http\:\/\/www\.w3\.org\/1999\/xlink"/)){
    source = source.replace(/^<svg/, '<svg xmlns:xlink="http://www.w3.org/1999/xlink"');
}

//add xml declaration
source = '<?xml version="1.0" standalone="no"?>\r\n' + source;

//convert svg source to URI data scheme.
var url = "data:image/svg+xml;charset=utf-8,"+encodeURIComponent(source);

//set url value to a element's href attribute.
document.getElementById("link").href = url;
//you can download svg file by right click menu.

I know this has already been answered, and that answer works well most of the time. However I found that it failed on Chrome (but not Firefox) if the svg image was large-ish (about 1MB). It works if you go back to using a Blob construct, as described here and here. The only difference is the type argument. In my code I wanted a single button press to download the svg for the user, which I accomplished with:

var svgData = $("#figureSvg")[0].outerHTML;
var svgBlob = new Blob([svgData], {type:"image/svg+xml;charset=utf-8"});
var svgUrl = URL.createObjectURL(svgBlob);
var downloadLink = document.createElement("a");
downloadLink.href = svgUrl;
downloadLink.download = "newesttree.svg";
document.body.appendChild(downloadLink);
downloadLink.click();
document.body.removeChild(downloadLink);

October 2019 edit: Comments have indicated that this code will work even without appending downloadLink to document.body and subsequently removing it after click(). I believe that used to work on Firefox, but as of now it no longer does (Firefox requires that you append and then remove downloadLink). The code works on Chrome either way.

Combining Dave's and defghi1977 answers. Here is a reusable function:

function saveSvg(svgEl, name) {
    svgEl.setAttribute("xmlns", "http://www.w3.org/2000/svg");
    var svgData = svgEl.outerHTML;
    var preface = '<?xml version="1.0" standalone="no"?>\r\n';
    var svgBlob = new Blob([preface, svgData], {type:"image/svg+xml;charset=utf-8"});
    var svgUrl = URL.createObjectURL(svgBlob);
    var downloadLink = document.createElement("a");
    downloadLink.href = svgUrl;
    downloadLink.download = name;
    document.body.appendChild(downloadLink);
    downloadLink.click();
    document.body.removeChild(downloadLink);
}

Invocation example:

saveSvg(svg, 'test.svg')