Simplify pdf.js logic

Instead of complicated splicing, we can simply return all pages.
Promise.all will take care of the correct ordering for us.

app/assets/javascripts/pdf/index.vue

@@ -14,7 +14,6 @@ export default {
   },
   data() {
     return {
-      loading: false,
       pages: [],
     };
   },
@@ -37,23 +36,18 @@ export default {
       return pdfjsLib
         .getDocument(this.document)
         .then(this.renderPages)
-        .then(() => this.$emit('pdflabload'))
-        .catch(error => this.$emit('pdflaberror', error))
-        .then(() => {
-          // Trigger a Vue update: https://vuejs.org/v2/guide/list.html#Caveats
-          this.pages.splice(this.pages.length);
-          this.loading = false;
+        .then(pages => {
+          this.pages = pages;
+          this.$emit('pdflabload');
+        })
+        .catch(error => {
+          this.$emit('pdflaberror', error);
         });
     },
     renderPages(pdf) {
       const pagePromises = [];
-      this.loading = true;
       for (let num = 1; num <= pdf.numPages; num += 1) {
-        pagePromises.push(
-          pdf.getPage(num).then(p => {
-            this.pages[p.pageIndex] = p;
-          }),
-        );
+        pagePromises.push(pdf.getPage(num));
       }
       return Promise.all(pagePromises);
     },
@@ -65,8 +59,8 @@ export default {
   <div v-if="hasPDF" class="pdf-viewer">
     <page
       v-for="(page, index) in pages"
+      v-if="page"
       :key="index"
-      :v-if="!loading"
       :page="page"
       :number="index + 1"
     />

app/assets/javascripts/pdf/page/index.vue

@@ -39,7 +39,9 @@ export default {
       .then(() => {
         this.rendering = false;
       })
-      .catch(error => this.$emit('pdflaberror', error));
+      .catch(error => {
+        this.$emit('pdflaberror', error);
+      });
   },
 };
 </script>