你可以看到,this就是window,也就是浏览器的全局对象。 在Understanding Variables, Scope, and Hoisting in JavaScript中,你学习到函数中的变量有自己的上下文。你可能会认为,在函数内部this会遵循相同的规则,但是并没有。顶层的函数中,this仍然指向全局对象。 你可以写一个顶层的函数,或者是一个没有
该this关键字是在JavaScript中一个非常重要的概念,也是一个特别令人迷惑的这两个新的开发者和那些谁拥有在其他编程语言的经验。在JavaScript中,this是对对象的引用。该对象this是指可以改变,含蓄地基于它是否是全球性的,在对象上,或者在一个构造函数,也可以明确地变化根据的使用Function原型方法bind,call和apply。 尽管...
call 、bind 、 apply 这三个函数的第一个参数都是 this 的指向对象,第二个参数差别就来了: call 的参数是直接放进去的,第二第三第 n 个参数全都用逗号分隔,直接放到后面obj.myFun.call(db,'成都', ... ,'string' )。 apply 的所有参数都必须放在一个数组里面传进去obj.myFun.apply(db,['成都', ....
到目前为止,我们知道JavaScript中的每一个函数都有两个方法:Call和Apply。这些方法可以被用来在函数内部设置this对象的内容,并内容传递给函数参数指向的对象。 Call takes the value to be used as the this object inside the function as the first parameter, and the remaining arguments to be passed to the ...
在下面的例子中,当调用 greet 方法的时候,该方法的this值会绑定到 obj 对象。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 functiongreet(){varreply=[this.animal,'typically sleep between',this.sleepDuration].join(' ');console.log(reply);}varobj={animal:'cats',sleepDuration:'12 and 16 ho...
A callback function in JavaScript is a function that is passed as an argument to another function and is invoked after some kind of event.
The apply method calls a function with a given this value and arguments provided as an array. Just like call you can write a method once and the inherit it in another object, without having to rewrite the method for the new object. ...
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. See Also: The JavaScriptthisTutorial ...
This has slightly less overhead than making asynchronous calls and can result in fewer render cycles because there's no intermediate state while awaiting results.To make a synchronous call from .NET to JavaScript in a client-side component, cast IJSRuntime to IJSInProcessRuntime to make ...
Creates a new instance of this class and initializes it with values from a JSON object generated from an ArcGIS product. The object passed into the input json parameter often comes from a response to a query operation in the REST API or a toJSON() method from another ArcGIS product. See...