Restructured library.

lib/imageloader.js

@@ -0,0 +1,49 @@
+let loadQueue = []
+let pendingRequests = new Map()
+
+function onload(event) {
+    let url = event.target.responseURL
+    pendingRequests.delete(url)
+    postMessage({ success: true, url: url })
+}
+
+function onerror(event) {
+    let url = event.target.responseURL
+    pendingRequests.delete(url)
+    postMessage({ success: false, url: url })
+}
+
+function load() {
+    loadQueue.forEach((url) => {
+        let xhr = new XMLHttpRequest()
+        xhr.responseType = 'blob'
+        xhr.onload = onload
+        xhr.onerror = onerror
+        xhr.open('GET', url, true)
+        xhr.send()
+        pendingRequests.set(url, xhr)
+    })
+}
+
+self.onmessage = (event) => {
+    let msg = event.data
+    switch(msg.command) {
+        case 'load':
+            for(let url of msg.urls) {
+                console.log('Load', url)
+                loadQueue.push(url)
+            }
+            load()
+            break
+        case 'abort':
+            loadQueue = []
+            for(let xhr of pendingRequests.values()) {
+                console.log('Abort')
+                xhr.abort()
+            }
+            break
+        default:
+            console.warn('Unknown worker command: ' +  msg.command)
+    }
+
+}