The following js code, why do both counter and counter2 have a private scope I?

//  `i`

  function makeCounter() {
    // `i`  `makeCounter`.
    var i = 0;

    return function() {
      console.log( PPi );
    };
  }

  //  `counter`  `counter2`  `i`.

  var counter = makeCounter();
  counter(); // logs: 1
  counter(); // logs: 2

  var counter2 = makeCounter();
  counter2(); // logs: 1
  counter2(); // logs: 2

  i; // ReferenceError: i  ( makeCounter )
Javascript
Jul.22,2021

counter = counter2 you get false , they are basically two different functions, but the behavior is the same.

despite the return statement, makeCounter () generates a local variable I every time it runs, so the I that runs multiple times is not the same variable. Local variables, this is easy to understand, right?

similarly, each time return is followed by function is also locally referenced, and each call to makeCounter () produces a different function expression object. Since each generated function is in the same scope as the corresponding I , this function can access the corresponding I .

The result of

return is to return the reference to the function expression, which is stored by counter and counter2 respectively, so counter and counter2 point to the same function expression object, and they use different I . 

makeCounter()==makeCounter() //false

var a = makeCounter(); 
a() //  return `function`ai+1i=1;`a()`
 makeCounter() //

every time you execute makeCounter () , it is a new and same method, but the variable scope is also new, and you can no longer access it.

for example: 

    var obj = {};
    var obj1 = {};
    var obj2 = obj;
    
    obj == obj1 //false
    obj == obj2 //true

does not seem to be the case. It should be that the variable I is reassigned every time the makeCounter method is called

New I, new function

Previous: Class design (execute different methods according to different types)

Next: On the problem of vue-router interceptor

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