Return empty a empty stream for zero sized blob (#86)

Return empty a empty stream for zero sized blob

.codecov.yml

@@ -0,0 +1,6 @@
+coverage:
+  round: up
+  precision: 2
+  parsers:
+    javascript:
+      enable_partials: yes

.github/workflows/ci.yml

@@ -0,0 +1,56 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    paths:
+      - "**.js"
+      - "package.json"
+      - ".github/workflows/ci.yml"
+
+jobs:
+  test:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+        node: ["15", "14", "12", engines]
+        exclude:
+          # On Windows, run tests with only the LTS environments.
+          - os: windows-latest
+            node: engines
+          - os: windows-latest
+            node: "14"
+          # On macOS, run tests with only the LTS environments.
+          - os: macOS-latest
+            node: engines
+          - os: macOS-latest
+            node: "14"
+
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Get Node.JS version from package.json
+        if: matrix.node == 'engines'
+        id: get-version
+        run: echo ::set-output name=node::$(npx --q minimum-node-version)
+
+      - uses: actions/setup-node@v2-beta
+        if: matrix.node != 'engines'
+        with:
+          node-version: ${{ matrix.node }}
+
+      - uses: actions/setup-node@v2-beta
+        if: matrix.node == 'engines'
+        with:
+          node-version: ${{steps.get-version.outputs.node}}
+
+      - run: npm install
+
+      - run: npm run report -- --colors
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v1
+        with:
+          file: ./coverage/coverage-final.json

.github/workflows/lint.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  pull_request:
+    paths:
+      - "**.js"
+      - "**eslint**"
+      - "package.json"
+      - ".github/workflows/lint.yml"
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js
+        uses: actions/setup-node@v2-beta
+        with:
+          node-version: 14
+      - run: npm install
+      - run: npm run lint

.gitignore

@@ -1,3 +1,8 @@
+# Lock files
+
+package-lock.json
+yarn.lock
+
 # Logs
 logs
 *.log
@@ -57,5 +62,5 @@ typings/
 # dotenv environment variables file
 .env
 
-# next.js build output
-.next
+index.d.ts
+from.d.ts

.npmrc

@@ -0,0 +1,2 @@
+package-lock=false
+save-exact=false

.travis.yml

@@ -1,11 +0,0 @@
-language: node_js
-node_js:
-  - "8"
-  - "10"
-  - "12"
-  - "node"
-script:
-  - npm run coverage
-cache:
-  directories:
-    - node_modules

CHANGELOG.md

@@ -1,14 +1,48 @@
-
 Changelog
 =========
 
+## next
+- Fixed a bug where in BlobDataItem when the file was empty (#86)
+
+## v2.1.2
+- Fixed a bug where `start` in BlobDataItem was undefined (#85)
+
+## v2.1.1
+- Add nullish values checking in Symbol.hasInstance (#82)
+- Add generated typings for from.js file (#80)
+- Updated dev dependencies
+
+## v2.1.0
+- Fix: .slice has an implementation bug (#54).
+- Added blob backed up by filesystem (#55)
+
+## v2.0.1
+
+- Fix: remove upper bound for node engine semver (#49).
+
+## v2.0.0
+
+> Note: This release was previously published as `1.0.7`, but as it contains breaking changes, we renamed it to `2.0.0`.
+
+- **Breaking:** minimum supported Node.js version is now 10.17.
+- **Breaking:** `buffer` option has been removed.
+- Enhance: create TypeScript declarations from JSDoc (#45).
+- Enhance: operate on blob parts (byte sequence) (#44).
+- Enhance: use a `WeakMap` for private properties (#42) .
+- Other: update formatting.
+
+## v1.0.6
+
+- Enhance: use upstream Blob directly in typings (#38)
+- Other: update dependencies
+
 ## v1.0.5
 
 - Other: no change to code, update dev dependency to address vulnerability reports
 
 ## v1.0.4
 
-- Other: general code revwrite to pass linting, prepare for `node-fetch` release v3
+- Other: general code rewrite to pass linting, prepare for `node-fetch` release v3
 
 ## v1.0.3
 

README.md

@@ -1,38 +1,57 @@
-
-fetch-blob
-==========
+# fetch-blob
 
 [![npm version][npm-image]][npm-url]
-[![build status][travis-image]][travis-url]
+[![build status][ci-image]][ci-url]
 [![coverage status][codecov-image]][codecov-url]
 [![install size][install-size-image]][install-size-url]
 
-A Blob implementation on node.js, originally from node-fetch
+A Blob implementation in Node.js, originally from [node-fetch](https://github.com/node-fetch/node-fetch).
 
-## Usage
+## Installation
 
 ```sh
-$ npm install fetch-blob
+npm install fetch-blob
 ```
 
+## Usage
+
 ```js
 const Blob = require('fetch-blob');
 const fetch = require('node-fetch');
+
 fetch('https://httpbin.org/post', {
     method: 'POST',
-        body: new Blob(['hello'], { type: 'text/plain' })
+    body: new Blob(['Hello World'], { type: 'text/plain' })
 })
-    .then(res => res.json()) // expecting a json response
+    .then(res => res.json());
     .then(json => console.log(json));
 ```
 
-See [MDN doc](https://developer.mozilla.org/en-US/docs/Web/API/Blob) and [Tests](https://github.com/bitinn/fetch-blob/blob/master/test.js) for more details.
+### Blob part backed up by filesystem
+To use, install [domexception](https://github.com/jsdom/domexception).
+
+```sh
+npm install fetch-blob domexception
+```
+
+```js
+const blobFrom = require('fetch-blob/from.js');
+const blob1 = blobFrom('./2-GiB-file.bin');
+const blob2 = blobFrom('./2-GiB-file.bin');
+
+// Not a 4 GiB memory snapshot, just holds 3 references
+// points to where data is located on the disk
+const blob = new Blob([blob1, blob2]);
+console.log(blob.size) // 4 GiB
+```
+
+See the [MDN documentation](https://developer.mozilla.org/en-US/docs/Web/API/Blob) and [tests](https://github.com/node-fetch/fetch-blob/blob/master/test.js) for more details.
 
 [npm-image]: https://flat.badgen.net/npm/v/fetch-blob
 [npm-url]: https://www.npmjs.com/package/fetch-blob
-[travis-image]: https://flat.badgen.net/travis/bitinn/fetch-blob
-[travis-url]: https://travis-ci.org/bitinn/fetch-blob
-[codecov-image]: https://flat.badgen.net/codecov/c/github/bitinn/fetch-blob/master
-[codecov-url]: https://codecov.io/gh/bitinn/fetch-blob
+[ci-image]: https://github.com/node-fetch/fetch-blob/workflows/CI/badge.svg
+[ci-url]: https://github.com/node-fetch/fetch-blob/actions
+[codecov-image]: https://flat.badgen.net/codecov/c/github/node-fetch/fetch-blob/master
+[codecov-url]: https://codecov.io/gh/node-fetch/fetch-blob
 [install-size-image]: https://flat.badgen.net/packagephobia/install/fetch-blob
 [install-size-url]: https://packagephobia.now.sh/result?p=fetch-blob

blob.js

@@ -1,135 +0,0 @@
-// Based on https://github.com/tmpvar/jsdom/blob/aa85b2abf07766ff7bf5c1f6daafb3726f2f2db5/lib/jsdom/living/blob.js
-// (MIT licensed)
-
-const Stream = require('stream');
-
-// Fix for "Readable" isn't a named export issue
-const {Readable} = Stream;
-
-const BUFFER = Symbol('buffer');
-const TYPE = Symbol('type');
-
-class Blob {
-	constructor(...args) {
-		this[TYPE] = '';
-
-		const blobParts = args[0];
-		const options = args[1];
-
-		const buffers = [];
-		/* eslint-disable-next-line no-unused-vars */
-		let size = 0;
-
-		if (blobParts) {
-			blobParts.forEach(element => {
-				let buffer;
-				if (element instanceof Buffer) {
-					buffer = element;
-				} else if (ArrayBuffer.isView(element)) {
-					buffer = Buffer.from(element.buffer, element.byteOffset, element.byteLength);
-				} else if (element instanceof ArrayBuffer) {
-					buffer = Buffer.from(element);
-				} else if (element instanceof Blob) {
-					buffer = element[BUFFER];
-				} else {
-					buffer = Buffer.from(typeof element === 'string' ? element : String(element));
-				}
-
-				size += buffer.length;
-				buffers.push(buffer);
-			});
-		}
-
-		this[BUFFER] = Buffer.concat(buffers);
-
-		const type = options && options.type !== undefined && String(options.type).toLowerCase();
-		if (type && !/[^\u0020-\u007E]/.test(type)) {
-			this[TYPE] = type;
-		}
-
-		if (options && Buffer.isBuffer(options.buffer)) {
-			this[BUFFER] = options.buffer;
-		}
-	}
-
-	get size() {
-		return this[BUFFER].length;
-	}
-
-	get type() {
-		return this[TYPE];
-	}
-
-	text() {
-		return Promise.resolve(this[BUFFER].toString());
-	}
-
-	arrayBuffer() {
-		const buf = this[BUFFER];
-		const ab = buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength);
-		return Promise.resolve(ab);
-	}
-
-	stream() {
-		const readable = new Readable();
-		readable._read = () => { };
-		readable.push(this[BUFFER]);
-		readable.push(null);
-		return readable;
-	}
-
-	toString() {
-		return '[object Blob]';
-	}
-
-	slice(...args) {
-		const {size} = this;
-
-		const start = args[0];
-		const end = args[1];
-		let relativeStart;
-		let relativeEnd;
-
-		if (start === undefined) {
-			relativeStart = 0;
-		} else if (start < 0) {
-			relativeStart = Math.max(size + start, 0);
-		} else {
-			relativeStart = Math.min(start, size);
-		}
-
-		if (end === undefined) {
-			relativeEnd = size;
-		} else if (end < 0) {
-			relativeEnd = Math.max(size + end, 0);
-		} else {
-			relativeEnd = Math.min(end, size);
-		}
-
-		const span = Math.max(relativeEnd - relativeStart, 0);
-
-		const buffer = this[BUFFER];
-		const slicedBuffer = buffer.slice(
-			relativeStart,
-			relativeStart + span
-		);
-		const blob = new Blob([], {type: args[2]});
-		blob[BUFFER] = slicedBuffer;
-		return blob;
-	}
-}
-
-Object.defineProperties(Blob.prototype, {
-	size: {enumerable: true},
-	type: {enumerable: true},
-	slice: {enumerable: true}
-});
-
-Object.defineProperty(Blob.prototype, Symbol.toStringTag, {
-	value: 'Blob',
-	writable: false,
-	enumerable: false,
-	configurable: true
-});
-
-module.exports = Blob;

from.js

@@ -0,0 +1,61 @@
+const {statSync, createReadStream} = require('fs');
+const Blob = require('./index.js');
+const DOMException = require('domexception');
+
+/**
+ * @param {string} path filepath on the disk
+ * @returns {Blob}
+ */
+function blobFrom(path) {
+	const {size, mtime} = statSync(path);
+	const blob = new BlobDataItem({path, size, mtime});
+
+	return new Blob([blob]);
+}
+
+/**
+ * This is a blob backed up by a file on the disk
+ * with minium requirement
+ *
+ * @private
+ */
+class BlobDataItem {
+	constructor(options) {
+		this.size = options.size;
+		this.path = options.path;
+		this.start = options.start || 0;
+		this.mtime = options.mtime;
+	}
+
+	// Slicing arguments is first validated and formated
+	// to not be out of range by Blob.prototype.slice
+	slice(start, end) {
+		return new BlobDataItem({
+			path: this.path,
+			start,
+			mtime: this.mtime,
+			size: end - start
+		});
+	}
+
+	stream() {
+		if (statSync(this.path).mtime > this.mtime) {
+			throw new DOMException('The requested file could not be read, typically due to permission problems that have occurred after a reference to a file was acquired.', 'NotReadableError');
+		}
+
+		if (!this.size) {
+			return new Blob().stream();
+		}
+
+		return createReadStream(this.path, {
+			start: this.start,
+			end: this.start + this.size - 1
+		});
+	}
+
+	get [Symbol.toStringTag]() {
+		return 'Blob';
+	}
+}
+
+module.exports = blobFrom;

index.js

@@ -0,0 +1,180 @@
+const {Readable} = require('stream');
+
+/**
+ * @type {WeakMap<Blob, {type: string, size: number, parts: (Blob | Buffer)[] }>}
+ */
+const wm = new WeakMap();
+
+async function * read(parts) {
+	for (const part of parts) {
+		if ('stream' in part) {
+			yield * part.stream();
+		} else {
+			yield part;
+		}
+	}
+}
+
+class Blob {
+	/**
+	 * The Blob() constructor returns a new Blob object. The content
+	 * of the blob consists of the concatenation of the values given
+	 * in the parameter array.
+	 *
+	 * @param {(ArrayBufferLike | ArrayBufferView | Blob | Buffer | string)[]} blobParts
+	 * @param {{ type?: string }} [options]
+	 */
+	constructor(blobParts = [], options = {}) {
+		let size = 0;
+
+		const parts = blobParts.map(element => {
+			let buffer;
+			if (element instanceof Buffer) {
+				buffer = element;
+			} else if (ArrayBuffer.isView(element)) {
+				buffer = Buffer.from(element.buffer, element.byteOffset, element.byteLength);
+			} else if (element instanceof ArrayBuffer) {
+				buffer = Buffer.from(element);
+			} else if (element instanceof Blob) {
+				buffer = element;
+			} else {
+				buffer = Buffer.from(typeof element === 'string' ? element : String(element));
+			}
+
+			// eslint-disable-next-line unicorn/explicit-length-check
+			size += buffer.length || buffer.size || 0;
+			return buffer;
+		});
+
+		const type = options.type === undefined ? '' : String(options.type).toLowerCase();
+
+		wm.set(this, {
+			type: /[^\u0020-\u007E]/.test(type) ? '' : type,
+			size,
+			parts
+		});
+	}
+
+	/**
+	 * The Blob interface's size property returns the
+	 * size of the Blob in bytes.
+	 */
+	get size() {
+		return wm.get(this).size;
+	}
+
+	/**
+	 * The type property of a Blob object returns the MIME type of the file.
+	 */
+	get type() {
+		return wm.get(this).type;
+	}
+
+	/**
+	 * The text() method in the Blob interface returns a Promise
+	 * that resolves with a string containing the contents of
+	 * the blob, interpreted as UTF-8.
+	 *
+	 * @return {Promise<string>}
+	 */
+	async text() {
+		return Buffer.from(await this.arrayBuffer()).toString();
+	}
+
+	/**
+	 * The arrayBuffer() method in the Blob interface returns a
+	 * Promise that resolves with the contents of the blob as
+	 * binary data contained in an ArrayBuffer.
+	 *
+	 * @return {Promise<ArrayBuffer>}
+	 */
+	async arrayBuffer() {
+		const data = new Uint8Array(this.size);
+		let offset = 0;
+		for await (const chunk of this.stream()) {
+			data.set(chunk, offset);
+			offset += chunk.length;
+		}
+
+		return data.buffer;
+	}
+
+	/**
+	 * The Blob interface's stream() method is difference from native
+	 * and uses node streams instead of whatwg streams.
+	 *
+	 * @returns {Readable} Node readable stream
+	 */
+	stream() {
+		return Readable.from(read(wm.get(this).parts));
+	}
+
+	/**
+	 * The Blob interface's slice() method creates and returns a
+	 * new Blob object which contains data from a subset of the
+	 * blob on which it's called.
+	 *
+	 * @param {number} [start]
+	 * @param {number} [end]
+	 * @param {string} [type]
+	 */
+	slice(start = 0, end = this.size, type = '') {
+		const {size} = this;
+
+		let relativeStart = start < 0 ? Math.max(size + start, 0) : Math.min(start, size);
+		let relativeEnd = end < 0 ? Math.max(size + end, 0) : Math.min(end, size);
+
+		const span = Math.max(relativeEnd - relativeStart, 0);
+		const parts = wm.get(this).parts.values();
+		const blobParts = [];
+		let added = 0;
+
+		for (const part of parts) {
+			const size = ArrayBuffer.isView(part) ? part.byteLength : part.size;
+			if (relativeStart && size <= relativeStart) {
+				// Skip the beginning and change the relative
+				// start & end position as we skip the unwanted parts
+				relativeStart -= size;
+				relativeEnd -= size;
+			} else {
+				const chunk = part.slice(relativeStart, Math.min(size, relativeEnd));
+				blobParts.push(chunk);
+				added += ArrayBuffer.isView(chunk) ? chunk.byteLength : chunk.size;
+				relativeStart = 0; // All next sequental parts should start at 0
+
+				// don't add the overflow to new blobParts
+				if (added >= span) {
+					break;
+				}
+			}
+		}
+
+		const blob = new Blob([], {type: String(type).toLowerCase()});
+		Object.assign(wm.get(blob), {size: span, parts: blobParts});
+
+		return blob;
+	}
+
+	get [Symbol.toStringTag]() {
+		return 'Blob';
+	}
+
+	static [Symbol.hasInstance](object) {
+		return (
+			object &&
+			typeof object === 'object' &&
+			typeof object.stream === 'function' &&
+			object.stream.length === 0 &&
+			typeof object.constructor === 'function' &&
+			/^(Blob|File)$/.test(object[Symbol.toStringTag])
+		);
+	}
+}
+
+Object.defineProperties(Blob.prototype, {
+	size: {enumerable: true},
+	type: {enumerable: true},
+	slice: {enumerable: true}
+});
+
+module.exports = Blob;

package.json

@@ -1,32 +1,69 @@
 {
     "name": "fetch-blob",
-  "version": "1.0.5",
-  "description": "A Blob implementation on node.js, originally from node-fetch",
-  "main": "blob.js",
+    "version": "2.1.2",
+    "description": "A Blob implementation in Node.js, originally from node-fetch.",
+    "main": "index.js",
+    "files": [
+        "from.js",
+        "index.js",
+        "index.d.ts",
+        "from.d.ts"
+    ],
     "scripts": {
-    "test": "ava",
-    "report": "nyc ava",
-    "coverage": "nyc --reporter json --reporter text ava && codecov -f coverage/coverage-final.json"
-  },
-  "repository": {
-    "type": "git",
-    "url": "git+https://github.com/bitinn/fetch-blob.git"
+        "lint": "xo",
+        "test": "xo && ava",
+        "report": "c8 --reporter json --reporter text ava",
+        "coverage": "c8 --reporter json --reporter text ava && codecov -f coverage/coverage-final.json",
+        "prepublishOnly": "tsc --declaration --emitDeclarationOnly --allowJs index.js from.js"
     },
+    "repository": "https://github.com/node-fetch/fetch-blob.git",
     "keywords": [
         "blob",
         "node-fetch"
     ],
+    "engines": {
+        "node": "^10.17.0 || >=12.3.0"
+    },
     "author": "David Frank",
     "license": "MIT",
     "bugs": {
-    "url": "https://github.com/bitinn/fetch-blob/issues"
+        "url": "https://github.com/node-fetch/fetch-blob/issues"
+    },
+    "homepage": "https://github.com/node-fetch/fetch-blob#readme",
+    "xo": {
+        "rules": {
+            "unicorn/import-index": "off",
+            "import/extensions": [
+                "error",
+                "always",
+                {
+                    "ignorePackages": true
+                }
+            ]
+        },
+        "overrides": [
+            {
+                "files": "test.js",
+                "rules": {
+                    "node/no-unsupported-features/es-syntax": 0,
+                    "node/no-unsupported-features/node-builtins": 0
+                }
+            }
+        ]
+    },
+    "peerDependenciesMeta": {
+        "domexception": {
+            "optional": true
+        }
     },
-  "homepage": "https://github.com/bitinn/fetch-blob#readme",
     "devDependencies": {
-    "ava": "^1.4.1",
-    "codecov": "^3.6.1",
-    "get-stream": "^5.1.0",
-    "node-fetch": "^2.6.0",
-    "nyc": "^14.1.1"
+        "ava": "^3.15.0",
+        "c8": "^7.7.1",
+        "codecov": "^3.8.1",
+        "domexception": "^2.0.1",
+        "get-stream": "^6.0.1",
+        "node-fetch": "^2.6.1",
+        "typescript": "^4.2.4",
+        "xo": "^0.38.2"
     }
 }

test.js

@@ -1,87 +1,195 @@
+const fs = require('fs');
+const test = require('ava');
+const getStream = require('get-stream');
+const {Response} = require('node-fetch');
+const {TextDecoder} = require('util');
+const Blob = require('./index.js');
+const blobFrom = require('./from.js');
 
-import test from 'ava';
-import Blob from './blob';
-import util from 'util';
-import stream from 'stream';
-import getStream from 'get-stream';
-import { Response } from 'node-fetch';
-
-const TextDecoder = util.TextDecoder;
-const Readable = stream.Readable;
-
-test('Blob ctor', t => {
-	let data = 'a=1';
-	let blob = new Blob([data]);
+test('new Blob()', t => {
+	const blob = new Blob(); // eslint-disable-line no-unused-vars
 	t.pass();
 });
 
+test('new Blob(parts)', t => {
+	const data = 'a=1';
+	const blob = new Blob([data]); // eslint-disable-line no-unused-vars
+	t.pass();
+});
+
+test('Blob ctor parts', async t => {
+	const parts = [
+		'a',
+		new Uint8Array([98]),
+		new Uint16Array([25699]),
+		new Uint8Array([101]).buffer,
+		Buffer.from('f'),
+		new Blob(['g']),
+		{}
+	];
+
+	const blob = new Blob(parts);
+	t.is(await blob.text(), 'abcdefg[object Object]');
+});
+
 test('Blob size', t => {
-	let data = 'a=1';
-	let blob = new Blob([data]);
+	const data = 'a=1';
+	const blob = new Blob([data]);
 	t.is(blob.size, data.length);
 });
 
 test('Blob type', t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
+	const type = 'text/plain';
+	const blob = new Blob([], {type});
 	t.is(blob.type, type);
 });
 
+test('Blob slice type', t => {
+	const type = 'text/plain';
+	const blob = new Blob().slice(0, 0, type);
+	t.is(blob.type, type);
+});
+
+test('invalid Blob type', t => {
+	const blob = new Blob([], {type: '\u001Ftext/plain'});
+	t.is(blob.type, '');
+});
+
+test('invalid Blob slice type', t => {
+	const blob = new Blob().slice(0, 0, '\u001Ftext/plain');
+	t.is(blob.type, '');
+});
+
 test('Blob text()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
 	t.is(await blob.text(), data);
 });
 
 test('Blob arrayBuffer()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
 
-	let decoder = new TextDecoder('utf-8');
-	let buffer = await blob.arrayBuffer();
+	const decoder = new TextDecoder('utf-8');
+	const buffer = await blob.arrayBuffer();
 	t.is(decoder.decode(buffer), data);
 });
 
 test('Blob stream()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
-	let result = await getStream(blob.stream());
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
+	const result = await getStream(blob.stream());
 	t.is(result, data);
 });
 
 test('Blob toString()', t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
 	t.is(blob.toString(), '[object Blob]');
 });
 
 test('Blob slice()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
-	let blob2 = blob.slice(0, 1);
-	t.is(await blob2.text(), data.slice(0, 1));
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice();
+	t.is(await blob.text(), data);
+});
+
+test('Blob slice(0, 1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(0, 1);
+	t.is(await blob.text(), 'a');
+});
+
+test('Blob slice(-1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(-1);
+	t.is(await blob.text(), 'h');
+});
+
+test('Blob slice(0, -1)', async t => {
+	const data = 'abcdefgh';
+	const blob = new Blob([data]).slice(0, -1);
+	t.is(await blob.text(), 'abcdefg');
+});
+
+test('Blob(["hello ", "world"]).slice(5)', async t => {
+	const parts = ['hello ', 'world'];
+	const blob = new Blob(parts);
+	t.is(await blob.slice(5).text(), ' world');
+});
+
+test('throw away unwanted parts', async t => {
+	const blob = new Blob(['a', 'b', 'c']).slice(1, 2);
+	t.is(await blob.text(), 'b');
 });
 
 test('Blob works with node-fetch Response.blob()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
-	let res = new Response(blob);
-	let blob2 = await res.blob();
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
+	const response = new Response(blob);
+	const blob2 = await response.blob();
 	t.is(await blob2.text(), data);
 });
 
 test('Blob works with node-fetch Response.text()', async t => {
-	let data = 'a=1';
-	let type = 'text/plain';
-	let blob = new Blob([data], { type });
-	let res = new Response(blob);
-	let text = await res.text();
+	const data = 'a=1';
+	const type = 'text/plain';
+	const blob = new Blob([data], {type});
+	const response = new Response(blob);
+	const text = await response.text();
 	t.is(text, data);
 });
+
+test('blob part backed up by filesystem', async t => {
+	const blob = blobFrom('./LICENSE');
+	t.is(await blob.slice(0, 3).text(), 'MIT');
+	t.is(await blob.slice(4, 11).text(), 'License');
+});
+
+test('Reading after modified should fail', async t => {
+	const blob = blobFrom('./LICENSE');
+	await new Promise(resolve => {
+		setTimeout(resolve, 100);
+	});
+	const now = new Date();
+	// Change modified time
+	fs.utimesSync('./LICENSE', now, now);
+	const error = await blob.text().catch(error => error);
+	t.is(error.name, 'NotReadableError');
+});
+
+test('Reading from the stream created by blobFrom', async t => {
+	const blob = blobFrom('./LICENSE');
+	const expected = await fs.promises.readFile('./LICENSE', 'utf-8');
+
+	const actual = await getStream(blob.stream());
+
+	t.is(actual, expected);
+});
+
+test('Reading empty blobs', async t => {
+	const blob = blobFrom('./LICENSE').slice(0, 0);
+	const actual = await blob.text();
+	t.is(actual, '');
+});
+
+test('Blob-ish class is an instance of Blob', t => {
+	class File {
+		stream() {}
+
+		get [Symbol.toStringTag]() {
+			return 'File';
+		}
+	}
+
+	t.true(new File() instanceof Blob);
+});
+
+test('Instanceof check returns false for nullish values', t => {
+	t.false(null instanceof Blob);
+});