add string tags for browser polyglot classes (#2214)

* add string tags

* set toStringTag property to configurable: true

CHANGELOG.md

@@ -14,6 +14,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 * Avoid calling virtual methods in constructors/destructors to avoid bypassing virtual dispatch. (#2229)
 * Remove unused private field `backend` in the `Backend` class. (#2229)
 ### Added
+* Added string tags to support class detection
 ### Fixed
 * Fix a case of use-after-free. (#2229)
 * Fix usage of garbage value by filling the allocated memory entirely with zeros if it's not modified. (#2229)

lib/bindings.js

@@ -4,10 +4,40 @@ const bindings = require('../build/Release/canvas.node')
 
 module.exports = bindings
 
+Object.defineProperty(bindings.Canvas.prototype, Symbol.toStringTag, {
+  value: 'HTMLCanvasElement',
+  configurable: true
+})
+
+Object.defineProperty(bindings.Image.prototype, Symbol.toStringTag, {
+  value: 'HTMLImageElement',
+  configurable: true
+})
+
 bindings.ImageData.prototype.toString = function () {
 	return '[object ImageData]'
 }
 
+Object.defineProperty(bindings.ImageData.prototype, Symbol.toStringTag, {
+  value: 'ImageData',
+  configurable: true
+})
+
 bindings.CanvasGradient.prototype.toString = function () {
 	return '[object CanvasGradient]'
 }
+
+Object.defineProperty(bindings.CanvasGradient.prototype, Symbol.toStringTag, {
+  value: 'CanvasGradient',
+  configurable: true
+})
+
+Object.defineProperty(bindings.CanvasPattern.prototype, Symbol.toStringTag, {
+  value: 'CanvasPattern',
+  configurable: true
+})
+
+Object.defineProperty(bindings.CanvasRenderingContext2d.prototype, Symbol.toStringTag, {
+  value: 'CanvasRenderingContext2d',
+  configurable: true
+})

test/canvas.test.js

@@ -1410,6 +1410,14 @@ describe('Canvas', function () {
     assert.strictEqual(pattern.toString(), '[object CanvasPattern]')
   })
 
+  it('CanvasPattern has class string of `CanvasPattern`', async function () {
+    const img = await loadImage(path.join(__dirname, '/fixtures/checkers.png'));
+    const canvas = createCanvas(20, 20)
+    const ctx = canvas.getContext('2d')
+    const pattern = ctx.createPattern(img)
+    assert.strictEqual(Object.prototype.toString.call(pattern), '[object CanvasPattern]')
+  })
+
   it('Context2d#createLinearGradient()', function () {
     const canvas = createCanvas(20, 1)
     const ctx = canvas.getContext('2d')
@@ -1439,6 +1447,11 @@ describe('Canvas', function () {
     assert.equal(0, imageData.data[i + 2])
     assert.equal(255, imageData.data[i + 3])
   })
+  it('Canvas has class string of `HTMLCanvasElement`', function () {
+    const canvas = createCanvas(20, 1)
+
+    assert.strictEqual(Object.prototype.toString.call(canvas), '[object HTMLCanvasElement]')
+  })
 
   it('CanvasGradient stringifies as [object CanvasGradient]', function () {
     const canvas = createCanvas(20, 1)
@@ -1447,6 +1460,13 @@ describe('Canvas', function () {
     assert.strictEqual(gradient.toString(), '[object CanvasGradient]')
   })
 
+  it('CanvasGradient has class string of `CanvasGradient`', function () {
+    const canvas = createCanvas(20, 1)
+    const ctx = canvas.getContext('2d')
+    const gradient = ctx.createLinearGradient(1, 1, 19, 1)
+    assert.strictEqual(Object.prototype.toString.call(gradient), '[object CanvasGradient]')
+  })
+
   describe('Context2d#putImageData()', function () {
     it('throws for invalid arguments', function () {
       const canvas = createCanvas(2, 1)
@@ -1943,7 +1963,7 @@ describe('Canvas', function () {
         ctx[k] = v
         ctx.restore()
         assert.strictEqual(ctx[k], old)
-  
+
         // save() doesn't modify the value:
         ctx[k] = v
         old = ctx[k]

test/image.test.js

@@ -30,6 +30,11 @@ describe('Image', function () {
     assert(Image.prototype.hasOwnProperty('width'))
   })
 
+  it('Image has class string of `HTMLImageElement`', async function () {
+    const img = new Image()
+    assert.strictEqual(Object.prototype.toString.call(img), '[object HTMLImageElement]')
+  })
+
   it('loads JPEG image', function () {
     return loadImage(jpgFace).then((img) => {
       assert.strictEqual(img.onerror, null)

test/imageData.test.js

@@ -17,6 +17,11 @@ describe('ImageData', function () {
     assert.strictEqual(imageData.toString(), '[object ImageData]')
   })
 
+  it('gives class string as `ImageData`', function () {
+    const imageData = createImageData(2, 3)
+    assert.strictEqual(Object.prototype.toString.call(imageData), '[object ImageData]')
+  })
+
   it('should throw with invalid numeric arguments', function () {
     assert.throws(() => { createImageData(0, 0) }, /width is zero/)
     assert.throws(() => { createImageData(1, 0) }, /height is zero/)

test/wpt/generated/the-canvas-element.js

@@ -171,6 +171,12 @@ describe("WPT: the-canvas-element", function () {
 		assert.strictEqual(window.CanvasRenderingContext2D.prototype.fill, undefined, "window.CanvasRenderingContext2D.prototype.fill", "undefined")
 	});
 
+	it("2d.type class string", function () {
+		const canvas = createCanvas(100, 50);
+		const ctx = canvas.getContext("2d");
+		assert.strictEqual(Object.prototype.toString.call(ctx), '[object CanvasRenderingContext2D]')
+	})
+
 	it("2d.type.replace", function () {
 		// Interface methods can be overridden
 		const canvas = createCanvas(100, 50);