与其他语言相比,函数的 this 关键字在 JavaScript 中的表现略有不同,此外,在严格模式和非严格模式之间也会有一些差别。
Unfortunately, the code above results in an error. The error occurs because this is set to Window in the setTimeout function. Window does not have a speakLeet method. One quick fix is to create a variable that stores the reference to the this. This variable is often called self or that...
//Create a global variable for context (this lives in the//global scope - window).varcontext = "Global (ie. window)";//Create an object.varobjectA ={ context:"Object A"};//Create another object.varobjectB ={ context:"Object B"};//--- ///--- ///Define a function that uses ...
08.alert(this.b);// 20 09.// also implicit via variable declaration 10.// because variable object of the global context 11.// is the global object itself 12.varc = 30; 13.alert(this.c);// 30 函数代码中的this值 在函数代码中使用this时很有趣,这种情况很难且会导致很多问题。 这种类型...
当JavaScript代码执行的时候,第一个进入的总是默认的Global Execution Context,所以说它总是在ECS的最底部。 对于每个Execution Context都有三个重要的属性,变量对象(Variable object,VO),作用域链(Scope chain)和this。这三个属性跟代码运行的行为有很重要的关系,下面会一一介绍。
So in the above example, this keyword in WhoIsThis() function will refer to window object. So, this.myVar will return 100. However, if you access myVar without this then it will refer to local myVar variable defined in WhoIsThis() function....
In a function, in strict mode,thisisundefined. In an event,thisrefers to theelementthat received the event. Methods likecall(),apply(), andbind()can referthistoany object. Note thisis not a variable. It is a keyword. You cannot change the value ofthis. ...
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但在JavaScript中,情况并非如此,即使在for循环完成后,变量i仍然在作用域内,在退出循环后仍保留其最后的值。(顺便说一下,这种行为被称为变量提升(variable hoisting)。 JavaScript中对块级作用域的支持是通过let关键字实现的。Let关键字已经被浏览器和Node.js等后端JavaScript引擎广泛支持了多年。
JavaScript In the example above, calling the functionsayHellowith thenewkeyword would immediately create a new object that is an instance of the functionsayHello. Thethisbinding inside the function body points to the new object that was created and assigned to the variableme. ...