implement cancellation for maplibre fetch [#1]

js/index.src.mjs

@@ -206,18 +206,22 @@ export const addProtocol = maplibre_instance => {
         let z = result[2]
         let x = result[3]
         let y = result[4]
+        var cancel = () => {}
         instance.getZxy(+z,+x,+y).then(val => {
             if (val) {
                 let headers = {'Range':'bytes=' + val[0] + '-' + (val[0]+val[1]-1)}
-                fetch(pmtiles_url,{headers:headers}).then(resp => {
+                const controller = new AbortController()
+                const signal = controller.signal
+                fetch(pmtiles_url,{signal:signal,headers:headers}).then(resp => {
                     return resp.arrayBuffer()
                 }).then(arr => {
                     callback(null,arr,null,null)
                 })
+                cancel = controller.abort
             } else {
                 callback(null,new Uint8Array(),null,null)
             }
         })
-         return { cancel: () => { console.log("Cancel not implemented") } }
+        return { cancel: cancel }
      })
 }