Given a filename for a static resource, returns the resource's absolute URL. Supports file paths with or without origin/protocol.

toAbsoluteURL.js

/**
 * Given a filename for a static resource, returns the resource's absolute
 * URL. Supports file paths with or without origin/protocol.
 */
function toAbsoluteURL (url) {
  // Handle absolute URLs (with protocol-relative prefix)
  // Example: //domain.com/file.png
  if (url.search(/^\/\//) != -1) {
    return window.location.protocol + url
  }

  // Handle absolute URLs (with explicit origin)
  // Example: http://domain.com/file.png
  if (url.search(/:\/\//) != -1) {
    return url
  }

  // Handle absolute URLs (without explicit origin)
  // Example: /file.png
  if (url.search(/^\//) != -1) {
    return window.location.origin + url
  }

  // Handle relative URLs
  // Example: file.png
  var base = window.location.href.match(/(.*\/)/)[0]
  return base + url
}