help explain why the output is 333 and aaa
function superClass () {
this.c =333;
this.d ="bbb";}
function subClass () {
this.c =222;
superClass.call(this);
this.d ="aaa";
console.log(this.c);//333
console.log(this.d);//aaa
}
subClass ();
help explain why the output is 333 and aaa
function superClass () {
this.c =333;
this.d ="bbb";}
function subClass () {
this.c =222;
superClass.call(this);
this.d ="aaa";
console.log(this.c);//333
console.log(this.d);//aaa
}
subClass ();
the this is all window, in the browser environment. This code is equivalent to modifying global variables in the order in which they are executed, and has nothing to do with call.
subClass (); is executed in the global environment, where the this points to window; superClass.call (this) here pass window to the function, and the this in it also points to window; window.c =222;
window.c =333;
window.d ='bbb';
window.d ='aaa';
console.log(window.c);//333
console.log(window.d);//aaaone. Simple statement about this: ignore the es6 arrow function and strict mode. Whoever calls this, points to him. For example:
var a = 2;
var obj = {
a:1,
get:function(){
console.log(this.a);
}
};
obj.get();//1
var fun = obj.get;
fun();//2
//thiswindowfunwindow,x(),thiswindows
//x.y(),thisx
//x.y.z(),thisytwo. Call/apply usage: call is similar to apply. I use call as an example
x.call(y,z);//y.x(z)thisyconclusion, such as the above two statements. Globally, this, in the browser means that both window.superClass (), c and d are tied to window, and the result is like the main result of the question.
Previous: Js reconstructs Mini Program's sharing method onShareAppMessage
Next: Does visual svn-server always report this error during installation?
what is the current level of support for vw,vh layouts in mobile browsers? ...
http: shrek.imdevsh.com demo. ask for help: the principle of inertia retardation effect in demo touchmove ...
I ve been looking for it for a long time, but I can t find it. 1. After the direct upload of web is completed, the server cannot know whether the file was uploaded successfully, who uploaded it, and the information of the file 2. Using web to dire...
for example, I request localhost:8080 a b c.cd proxy to http: www.aaaa.com api can you change a b c.cd to a b c , before proxy? means that the agent rewrites the original path before. ...
question 1. The project is a chat application, which needs to display the latest news in the chat window in real time. Using the scrollIntoView method id div for bottom, I want to put it at the bottom. As long as it can be displayed, other chat message...
var myNumber = { value: 1, add: function(i){ var helper = function(i){ console.log(this); this.value += i; } helper(i); } } myNumber.add(1); Why does this this point to window?? The add method called by the myNumber o...
Click the button to show that (Bing s daily wallpaper) is successful, and then when the background of the page changes, it takes time to render, and there will be a white background color. How to solve this? ...
1. Execute npm install-g pm2 2.pm2 pm2 start app.js pm2 3.ln -s root myapp pm2 usr local bin still failed to solve the problem messed up for a long time because no soft connection was created. ln -s root node-v8.9.0-linux-x64 lib node_...
want to use vue2.0 to develop a small web application for the company, running on the mobile side. How can the above functions be achieved? ...
vue.js implements specification selection on product details page Click to select version option and click to select color option. Highlight has been selected. How to display the selected version and color html Code < div class= "chose-ck " > : ...
ios embedded h5 page input box will not lose focus if you click on the blank space. The soft keyboard will not fold. what should I do? try to bind the click event to document. If the input box loses focus when you click, it is still invalid. ...
as shown in the figure, how to determine that the user clicked on this X, and execute the corresponding method. ...
var a = {0:"A",1:"B",2:"C",length:3}; var newa = Array.prototype.slice.call(a); console.log(newa); my understanding of this example is that the an object inherits and executes Array s slice method, but the slice method...
what s the difference between writing JavaScript code in a js file and writing code in < srcipt > < srcipt >? Why can I introduce other js files as require in the js file and do report an error in the < srcipt > tag . ...
Icon shows the red part. Choose how to write the effect in css ....
We are Mini Program s project. To get the code logged in by Wechat, request the backend api to get the sessionkey. But if it is a concurrent request, if it happens to expire at this time, and several requests go to get the sessionkey at the same time, t...
o ...
brief: because Mini Program s project uses wepy s framework, but you don t quite understand that the role of this interceptor is to integrate all the interfaces? Or? ...
win7 system, scaffolding vue-cli has been installed, there is a version, but the initialization project appears this hole, cannot verify this certificate? Please help ...
Mobile input focus cannot directly evoke the mobile phone keyboard, what is the related auxiliary operation? Simple H5 page, do not use any framework, how to automatically evoke the soft keyboard? ...