Add default FileAttachment implementation.

It always throws not found! Also fix FileAttachments(resolve) to throw an error
synchronously, rather than asynchronously, when the file does not exist.

Author: mbostock

src/fileAttachment.js

@@ -5,16 +5,14 @@ async function remote_fetch(file) {
 }
 
 class FileAttachment {
-  constructor(resolve, name) {
+  constructor(url, name) {
     Object.defineProperties(this, {
-      _resolve: {value: resolve},
+      _url: {value: url},
       name: {value: name, enumerable: true}
     });
   }
   async url() {
-    const url = await this._resolve(this.name);
-    if (url == null) throw new Error(`Unknown file: ${this.name}`);
-    return url;
+    return this._url;
   }
   async blob() {
     return (await remote_fetch(this)).blob();
@@ -45,6 +43,14 @@ class FileAttachment {
   }
 }
 
+export function NoFileAttachments(name) {
+  throw new Error(`File not found: ${name}`);
+}
+
 export default function FileAttachments(resolve) {
-  return (name) => new FileAttachment(resolve, name);
+  return name => {
+    const url = resolve(name += ""); // Returns a Promise, or null.
+    if (url == null) throw new Error(`File not found: ${name}`);
+    return new FileAttachment(url, name);
+  };
 }

src/library.js

@@ -1,6 +1,7 @@
 import constant from "./constant.js";
 import DOM from "./dom/index.js";
 import Files from "./files/index.js";
+import {NoFileAttachments} from "./fileAttachment.js";
 import Generators from "./generators/index.js";
 import html from "./html.js";
 import md from "./md.js";
@@ -17,6 +18,7 @@ export default function Library(resolver) {
   const require = requirer(resolver);
   Object.defineProperties(this, {
     DOM: {value: DOM, writable: true, enumerable: true},
+    FileAttachment: {value: constant(NoFileAttachments), writable: true, enumerable: true},
     Files: {value: Files, writable: true, enumerable: true},
     Generators: {value: Generators, writable: true, enumerable: true},
     html: {value: constant(html), writable: true, enumerable: true},

test/DOM/uid-test.js

@@ -0,0 +1,15 @@
+import {test} from "tap";
+import UID from "../../src/dom/uid.js";
+
+test("UID", t => {
+  global.location = "https://test.com/";
+  const hi = UID("hi");
+  t.deepEqual(hi, {
+    id: "O-hi-1",
+    href: "https://test.com/#O-hi-1"
+  });
+  t.equal(hi.toString(), "url(https://test.com/#O-hi-1)");
+  const anon = UID();
+  t.equal(anon.toString(), "url(https://test.com/#O-2)");
+  t.end();
+});

test/fileAttachments-test.js

@@ -0,0 +1,8 @@
+import {test} from "tap";
+import {FileAttachments} from "../src/index.js";
+
+test("FileAttachments is exported by stdlib", t => {
+  t.equal(typeof FileAttachments, "function");
+  t.equal(FileAttachments.name, "FileAttachments");
+  t.end();
+});

test/index-test.js

@@ -1,10 +1,10 @@
 import {test} from "tap";
-import {Library, FileAttachments} from "../src/index.js";
-import UID from "../src/dom/uid.js";
+import {Library} from "../src/index.js";
 
 test("new Library returns a library with the expected keys", async t => {
   t.deepEqual(Object.keys(new Library()).sort(), [
     "DOM",
+    "FileAttachment",
     "Files",
     "Generators",
     "Mutable",
@@ -20,22 +20,3 @@ test("new Library returns a library with the expected keys", async t => {
   ]);
   t.end();
 });
-
-test("FileAttachments is exported by stdlib/index", t => {
-  t.equal(typeof FileAttachments, "function");
-  t.equal(FileAttachments.name, "FileAttachments");
-  t.end();
-});
-
-test("UID", t => {
-  global.location = "https://test.com/";
-  const hi = UID("hi");
-  t.deepEqual(hi, {
-    id: "O-hi-1",
-    href: "https://test.com/#O-hi-1"
-  });
-  t.equal(hi.toString(), "url(https://test.com/#O-hi-1)");
-  const anon = UID();
-  t.equal(anon.toString(), "url(https://test.com/#O-2)");
-  t.end();
-});