Reduce the size of SVG files exported from Sketch

thin-svg.js

#!/usr/bin/env node

var DOMParser = require('xmldom').DOMParser;
var fs = require("fs");

var file = fs.readFileSync(process.argv[2], 'utf-8');
var doc = new DOMParser().parseFromString(file, 'text/xml');
var regex = /^\s*translate\( *(-?\d+\.?\d*) *, *(-?\d+\.?\d*) *\)\s*$/;

// pass 1: remove IDs

var recursiveRemoveId = function (element) {
    if (element.nodeType === 1) {
        if (element.hasAttribute('id')) {
            element.removeAttribute('id');
        }
    }
    Array.prototype.forEach.call(element.childNodes || [], recursiveRemoveId.bind(null));
};

recursiveRemoveId(doc);

// pass 2: merge stacked translates

var recursive = function (element) {
    var thisTransform, childTransform, childCount;
    if (element.nodeType === 1) {
        if (element.hasAttribute('transform')) {
            while (true) {
                thisTransform = element.getAttribute('transform').match(regex);
                childCount = Array.prototype.filter.call(element.childNodes || [], function (ct) { return ct.nodeType === 1; });
                if ((childCount.length === 1) && (childCount[0].attributes.length === 1) && childCount[0].hasAttribute('transform')) {
                    childTransform = childCount[0].getAttribute('transform').match(regex);
                    element.setAttribute('transform', 'translate(' + (parseFloat(thisTransform[1]) + parseFloat(childTransform[1])) + ',' + (parseFloat(thisTransform[2]) + parseFloat(childTransform[2])) + ')');
                    Array.prototype.forEach.call(childCount[0].childNodes, function (cn) {
                        element.appendChild(cn.cloneNode(true));
                    });
                    element.removeChild(childCount[0]);
                } else {
                    break;
                }
            }
        }
    }
    Array.prototype.forEach.call(element.childNodes || [], recursive.bind(null));
};

recursive(doc);

// pass 3: remove spaces and comments

var recursiveTrimSpace = function (element) {
    Array.prototype.forEach.call(element.childNodes || [], function (n) {
        if (n.nodeType === 3) { // text
            element.replaceChild(doc.createTextNode(n.data.trim()), n);
        } else if (n.nodeType === 8) { // comment
            element.removeChild(n);
        } else {
            recursiveTrimSpace(n);
        }
    });
};

recursiveTrimSpace(doc);

fs.writeFileSync('thin-' + process.argv[2], doc.toString());