Straighten out JavaScript (14)-constructor and instanceof

Let's repeat the previous example: It's a function. How can it become an object?

 
Function myobj (a, B) {This. X = A; this. y = B;} var OBJ = new myobj (11, 22); alert (obj. x); // 11 alert (obj. y); // 22 alert (typeof OBJ); // object // an object must be created through a constructor. It is not difficult to become an object with a constructor; // use the new keyword to call a function. Javascript creates an object and treats the function as a constructor of the object. // This is like the constructor of the string class. The constructor of the array class is array ()...

  
 

The name of the constructor of each class must be different. However, you can use constructor to refer to them.

 
VaR STR = new string (); alert (Str. constructor);/* will output the following: function string () {[native code]}, but it does not show us the specific implementation.Code, Only the custom one will see */var arr = new array (); alert (ARR. constructor);/* will output the following: Function Array () {[native code]} */function myobj (a, B) {This. X = A; this. y = B;} var OBJ = new myobj (11, 22); alert (obj. constructor);/* will output the following: function myobj (a, B) {This. X = A; this. y = B ;}*/

  
 

Determine the class to which an object belongs (method 1)

 
// The preceding method can be used to determine the VaR STR, arr, s; STR = new string (); alert (Str. constructor = string); // truearr = new array (); alert (ARR. constructor = array); // true/* but this may cause a problem. For example, if a string is not an object, true */S = 'abc'; alert (S. constructor = string); // true // The conditions can be added to solve this problem, but it is better to use the next method directly.

  
 

Determine the class to which an object belongs (Method 2: Use the instanceof keyword)

 
VaR STR, arr, STR; STR = new string (); alert (STR instanceof string); // truearr = new array (); alert (ARR instanceof array ); // truestr = 'abc'; alert (STR instanceof string); // false/* but this also has a problem, because the object is the ancestor of all classes... */STR = new string (); alert (STR instanceof object); // true