first pass at a css rel=preload polyfill workflow. Note: expects loadCSS function to be defined. #59

Author: scottjehl

src/cssrelpreload.js

@@ -0,0 +1,29 @@
+/* CSS rel=preload polyfill. Depends on loadCSS function */
+(function( w ){
+  // rel=preload support test
+  function support(){
+    try {
+      return w.document.createElement("link").relList.supports( "preload" );
+    } catch (e) {}
+  }
+  // loop preload links and fetch using loadCSS
+  function poly(){
+    var links = w.document.getElementsByTagName( "link" );
+    for( var i = 0; i < links.length; i++ ){
+      if( links[ i ].getAttribute( "rel" ) === "preload" ){
+        w.loadCSS( links[ i ].href, links[ i ] );
+        links[ i ].rel = null;
+      }
+    }
+  }
+  // if link[rel=preload] is not supported, we must fetch the CSS manually using loadCSS
+  if( !support() ){
+    poly();
+    var run = w.setInterval( poly, 300 );
+    if( w.addEventListener ){
+      w.addEventListener( "load", function(){
+        w.clearInterval( run );
+      } )
+    }
+  }
+}( this ));