An interview question for js

topic description 

var obj = {
   name:"zhangsan",
   sayName:function(){
     console.info(this.name);
   }
 }
 var wfunc = obj.sayName;
 obj.sayName();//zhangsan
 wfunc();//undefined
 var name = "lisi";
 obj.sayName();//zhangsan
 wfunc();//lisi

sources of topics and their own ideas

is mainly because I don"t know the reasons for the next three answers. I hope the boss can explain

.
Javascript
Jul.06,2022

the second is not undefined, but an empty string. Window comes with the name attribute

my understanding is:
/ declare variables first:
var obj,
var wfunc,
var name,
/ in the assignment
var obj= {}
var var wfunc = obj.sayName;
obj.sayName () / / this takes the value of name as zhangsan
wfunc () / / the this at this time points to the declared name in window,window, but is not defined, so this time is undefined
name= "lisi" / / at this time the name value is lisi
obj.sayName () / / this points to obj, so the value of name is zhangsan
wfunc () / / at this time this points to the name declared in window,window, and is assigned to lisi

when calling with obj , the object context of sayName is obj .
is re-assigned to wfunc before execution. The context object is window , but there is no name attribute on window . In addition, variables declared using var are promoted to global variables and are mounted under the window object by default, so the context object is still window , but the name attribute already exists. 

var wfunc = obj.sayName;   
//wfunc
wfunc = function () {
    console.log(this.name)   //thiswindow
} 
undefined

obj.sayName (); / / zhangsan / / this points to obj 

var name = "lisi";    //window.name = 'lisi'
obj.sayName();//zhangsan
wfunc();//lisi

Previous: A few small questions about git checkout-b and git push!

Next: Is there any front-end component that can write rules engine rules?

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
© 2021 CodesHelper
Advertising Contact us About us
Menu