在量角器中获取测量"this.TakeScreenshot is not a function "误差

Question

我在JS文件中编写了一个函数TakeScreenshot 说base.js保存屏幕截图并返回我屏幕截图路径的实现如下。

this.TakeScreenshot = function(screenShotName) {
//some stuff.....
        browser.takeScreenshot().then(function (png) {
            var stream = fs.createWriteStream(screenshotPath);
            stream.write(new Buffer(png, 'base64'));
            stream.end();
    });
        return screenshotPath;
    };
I am calling the above function in another function called "isTruelyPresent". This function will take a screenshot if element is present/not present on UI. The implementation is as below:
this.isTrulyPresent = function(elementToCheckVisibilityOf, element2) {
          return elementToCheckVisibilityOf.isDisplayed().then(function (isDisplayedd) {
          var myObj;
          myObj = this.TakeScreenshot(element2);
          // some stuff
          console.log('isDisplayed'+isDisplayedd);
          return isDisplayedd;
    }).then(null, function (error) {
          var myObj;
          myObj = this.TakeScreenshot("ErrorSS");
          console.log('A NoSuchElement exception was throw because the element is NOT displayed so we return false');
          return false;
        });  
    };

Protractor script is throwing an error "this.TakeScreenshot is not a function". Could any one please help me to resolve the issue.

Answer 1

首先要注意，isPresent(检查 DOM 中是否存在元素(和isDisplayed(检查元素是否存在于 DOM 中并且可见(之间存在差异。如果 DOM 中不存在某个元素，则方法isDisplayed()将严重失败。您现在正在捕获此错误，这也是您想要的吗？

其次，每个function都可以有自己的this范围。这意味着您的this.TakeScreenshot("ErrorSS")可以引用function(error){}的this范围，而不是要引用的this。

这 ;-(文档可能有助于解决此问题。我通常使用的是arrow函数，请参阅链接。