Deterministic filename-based CDN sharding

public_path.js

'use strict';

var publicPath = require('./static_path')(process.env.PUBLIC_PATH); // e.g. PUBLIC_PATH=https://static%d.domain.com/

module.exports = publicPath;

static_path.js

'use strict';

var staticPath = function (root, rootPattern, pathPattern) {
    if (rootPattern == null) {
        rootPattern = /%d/g;
    }
    if (pathPattern == null) {
        pathPattern = /^https?:\/\/.*?\/(.*)$/;
    }
    if (rootPattern.test(root)) {
        return function (path) {
            var match, hash, i, length, digit;
            if (path == null) {
                return root.replace(rootPattern, '');
            }
            else {
                match = path.match(pathPattern);
                if (match != null) {
                    path = match[1];
                }
                hash = 0;
                for (i = 0, length = path.length; i < length; i++) {
                    hash = (((hash << 5) - hash) + path.charCodeAt(i)) & 0xFFFFFFFF;
                }
                digit = Math.abs(hash % 10);
                return root.replace(rootPattern, digit) + path;
            }
        };
    }
    else {
        return function (path) {
            return (path == null) ? root : root + path;
        };
    }
};

module.exports = staticPath;