feat(ElementHandle): add ElementHandle.boxModel method (#2256)

This patch introduces ElementHandle.boxModel to get element's
box model.

Fixes #1357

docs/api.md

@@ -186,6 +186,7 @@
   * [elementHandle.$x(expression)](#elementhandlexexpression)
   * [elementHandle.asElement()](#elementhandleaselement)
   * [elementHandle.boundingBox()](#elementhandleboundingbox)
+  * [elementHandle.boxModel()](#elementhandleboxmodel)
   * [elementHandle.click([options])](#elementhandleclickoptions)
   * [elementHandle.contentFrame()](#elementhandlecontentframe)
   * [elementHandle.dispose()](#elementhandledispose)
@@ -2197,6 +2198,17 @@ The method evaluates the XPath expression relative to the elementHandle. If ther
 
 This method returns the bounding box of the element (relative to the main frame), or `null` if the element is not visible.
 
+#### elementHandle.boxModel()
+- returns: <[Promise]<?[Object]>>
+  - content <[Array]<[Object]>> Content box, represented as an array of {x, y} points.
+  - padding <[Array]<[Object]>> Padding box, represented as an array of {x, y} points.
+  - border <[Array]<[Object]>> Border box, represented as an array of {x, y} points.
+  - margin <[Array]<[Object]>> Margin box, represented as an array of {x, y} points.
+  - width <[number]> Element's width.
+  - height <[number]> Element's height.
+
+This method returns boxes of the element, or `null` if the element is not visible. Boxes are represented as an array of objects, {x, y} for each point, points clock-wise. See [getBoxModel](https://chromedevtools.github.io/devtools-protocol/tot/DOM#method-getBoxModel) for more details.
+
 #### elementHandle.click([options])
 - `options` <[Object]>
   - `button` <[string]> `left`, `right`, or `middle`, defaults to `left`.

lib/ElementHandle.js

@@ -79,6 +79,28 @@ class ElementHandle extends JSHandle {
     };
   }
 
+  /**
+   * @return {!Promise<?{model: object}>}
+   */
+  _getBoxModel() {
+    return this._client.send('DOM.getBoxModel', {
+      objectId: this._remoteObject.objectId
+    }).catch(error => debugError(error));
+  }
+
+  /**
+   * @param {!Array<number>} quad
+   * @return {!Array<object>}
+   */
+  _fromProtocolQuad(quad) {
+    return [
+      {x: quad[0], y: quad[1]},
+      {x: quad[2], y: quad[3]},
+      {x: quad[4], y: quad[5]},
+      {x: quad[6], y: quad[7]}
+    ];
+  }
+
   async hover() {
     const {x, y} = await this._visibleCenter();
     await this._page.mouse.move(x, y);
@@ -133,9 +155,7 @@ class ElementHandle extends JSHandle {
    * @return {!Promise<?{x: number, y: number, width: number, height: number}>}
    */
   async boundingBox() {
-    const result = await this._client.send('DOM.getBoxModel', {
+    const result = await this._getBoxModel();
-      objectId: this._remoteObject.objectId
-    }).catch(error => void debugError(error));
 
     if (!result)
       return null;
@@ -149,6 +169,26 @@ class ElementHandle extends JSHandle {
     return {x, y, width, height};
   }
 
+  /**
+   * @return {!Promise<?object>}
+   */
+  async boxModel() {
+    const result = await this._getBoxModel();
+
+    if (!result)
+      return null;
+
+    const {content, padding, border, margin, width, height} = result.model;
+    return {
+      content: this._fromProtocolQuad(content),
+      padding: this._fromProtocolQuad(padding),
+      border: this._fromProtocolQuad(border),
+      margin: this._fromProtocolQuad(margin),
+      width,
+      height
+    };
+  }
+
   /**
    * @return {!Promise<?{x: number, y: number, width: number, height: number}>}
    */

test/elementhandle.spec.js

@@ -52,6 +52,33 @@ module.exports.addTests = function({testRunner, expect}) {
     });
   });
 
+  describe('ElementHandle.boxModel', function() {
+    it('should work', async({page, server}) => {
+      const leftTop = {x: 28, y: 260};
+      const rightTop = {x: 292, y: 260};
+      const rightBottom = {x: 292, y: 278};
+      const leftBottom = {x: 28, y: 278};
+
+      await page.setViewport({width: 500, height: 500});
+      await page.goto(server.PREFIX + '/frames/nested-frames.html');
+      const nestedFrame = page.frames()[1].childFrames()[1];
+      const elementHandle = await nestedFrame.$('div');
+      const box = await elementHandle.boxModel();
+      expect(box.content).toEqual([leftTop, rightTop, rightBottom, leftBottom]);
+      expect(box.padding).toEqual([leftTop, rightTop, rightBottom, leftBottom]);
+      expect(box.border).toEqual([leftTop, rightTop, rightBottom, leftBottom]);
+      expect(box.margin).toEqual([leftTop, rightTop, rightBottom, leftBottom]);
+      expect(box.height).toBe(18);
+      expect(box.width).toBe(264);
+    });
+
+    it('should return null for invisible elements', async({page, server}) => {
+      await page.setContent('<div style="display:none">hi</div>');
+      const element = await page.$('div');
+      expect(await element.boxModel()).toBe(null);
+    });
+  });
+
   describe('ElementHandle.contentFrame', function() {
     it('should work', async({page,server}) => {
       await page.goto(server.EMPTY_PAGE);