# class:executioncontext ### class: ExecutionContext v0.9.0 該類表示一個 JavaScript 執行的上下文。 [Page](#?product=Puppeteer&version=v1.11.0&show=api-class-page "Page") 可能有許多執行上下文： - 每個 [frame](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe) 都有 "默認" 的執行上下文，它始終在將幀附加到 DOM 后創建。該上下文由 [`frame.executionContext()`](#?product=Puppeteer&version=v1.11.0&show=api-frameexecutioncontext) 方法返回。 - [Extensions](https://developer.chrome.com/extensions) 的內容腳本創建了其他執行上下文。 除了頁面，執行上下文可以在 [workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API) 中找到。 #### Methods - [executionContext.evaluate(pageFunction, ...args)](#?product=Puppeteer&version=v1.11.0&show=api-executioncontextevaluatepagefunction-args)v0.9.0 - [executionContext.evaluateHandle(pageFunction, ...args)](#?product=Puppeteer&version=v1.11.0&show=api-executioncontextevaluatehandlepagefunction-args)v0.9.0 - [executionContext.frame()](#?product=Puppeteer&version=v1.11.0&show=api-executioncontextframe)v0.9.0 - [executionContext.queryObjects(prototypeHandle)](#?product=Puppeteer&version=v1.11.0&show=api-executioncontextqueryobjectsprototypehandle)v0.9.0 ### Methods #### executionContext.evaluate(pageFunction, ...args)v0.9.0 - `pageFunction` <[function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function "Function")|[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type "String")> Function to be evaluated in `executionContext` - `...args` <...[Serializable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Description "Serializable")|[JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle")> Arguments to pass to `pageFunction` - returns: <[Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise "Promise")<[Serializable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Description "Serializable")>> Promise which resolves to the return value of `pageFunction` 如果傳遞給 `executionContext.evaluate` 的函數返回一個[Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise "Promise")，那么 `executionContext.evaluate` 將等待承諾解析并返回它的值。 ``` const executionContext = await page.mainFrame().executionContext();const result = await executionContext.evaluate(() => Promise.resolve(8 * 7));console.log(result); // 輸出 "56" ``` 入參可以是一個字符串，但不能是函數。 ``` console.log(await executionContext.evaluate('1 + 2')); // 輸出 "3" ``` [JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle") 實例可以作為參數傳遞給 `executionContext.evaluate`： ``` const oneHandle = await executionContext.evaluateHandle(() => 1);const twoHandle = await executionContext.evaluateHandle(() => 2);const result = await executionContext.evaluate((a, b) => a + b, oneHandle, twoHandle);await oneHandle.dispose();await twoHandle.dispose();console.log(result); // 輸出 '3' ``` #### executionContext.evaluateHandle(pageFunction, ...args)v0.9.0 - `pageFunction` <[function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function "Function")|[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type "String")> 函數在 `executionContext` 中被運行 - `...args` <...[Serializable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Description "Serializable")|[JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle")> 傳遞給 `pageFunction` 的參數 - returns: <[Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise "Promise")<[JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle")>> Promise which resolves to the return value of `pageFunction` as in-page object (JSHandle) `executionContext.evaluate` 和 `executionContext.evaluateHandle` 唯一的區別在于`executionContext.evaluateHandle` 會返回頁內對象（JSHandle）。 如果傳遞給 `executionContext.evaluateHandle` 的函數返回一個 [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise "Promise")，那么`executionContext.evaluateHandle`將等待承諾解析并返回它的值。 ``` const context = await page.mainFrame().executionContext();const aHandle = await context.evaluateHandle(() => Promise.resolve(self));aHandle; // 處理全局對象 ``` 入參可以是一個字符串，但不能是函數。 ``` const aHandle = await context.evaluateHandle('1 + 2'); // 處理'3'對象 ``` [JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle") 實例可以作為參數傳遞給 `executionContext.evaluateHandle`： ``` const aHandle = await context.evaluateHandle(() => document.body);const resultHandle = await context.evaluateHandle(body => body.innerHTML, aHandle);console.log(await resultHandle.jsonValue()); // 輸出 body 的 innerHTMLawait aHandle.dispose();await resultHandle.dispose(); ``` #### executionContext.frame()v0.9.0 - returns: <?[Frame](#?product=Puppeteer&version=v1.11.0&show=api-class-frame "Frame")> 與此執行上下文相關的框架。 > **注意** 并非每個執行的上下文都與框架有關系。 例如，workers 和擴展程序具有與框架無關的執行上下文。 #### executionContext.queryObjects(prototypeHandle)v0.9.0 - `prototypeHandle` <[JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle")> 對象原型的句柄 - returns: <[JSHandle](#?product=Puppeteer&version=v1.11.0&show=api-class-jshandle "JSHandle")> 這個原型的一個對象數組的句柄 該方法重復查找 JavaScript 堆，找到具有給定原型的所有對象。 ``` // 創建一個 Map 對象await page.evaluate(() => window.map = new Map());// 獲取 Map 對象原型的句柄const mapPrototype = await page.evaluateHandle(() => Map.prototype);// 將所有映射實例查詢到一個數組中const mapInstances = await page.queryObjects(mapPrototype);// 計算堆中映射對象的數量const count = await page.evaluate(maps => maps.length, mapInstances);await mapInstances.dispose();await mapPrototype.dispose(); ```  puppeteer.js中文網|class:executioncontext puppeteer.js中文文檔, puppeteer chrome, puppeteer firefox, puppeteer api 中文文檔 puppeteer.js中文網包含了Puppeteer中文文檔，最新資訊，應用案例等。Puppeteer 是一個 Node 庫，它提供了一個高級 API 來通過 DevTools 協議控制 Chromium 或 Chrome。