JavaScript functions call regular calls and are called with new

The return value of the JavaScript function

• The function returns all undefined without an explicit return value
• When the function has a definite return value:
  • If the function return value is a value type (number, Boolean, String) in the general sense, the new operator returns an instance object of the function;
  • If the function returns a reference type (Object, Array, function), the result of the direct call function is equated with the new operator;

The return value type of a function is a value type (number, Boolean, String):

 1  function   　　 person () { 2  var  name = ' Tom ' ;  3  return  ' Jack ' ; 4   5  6  var  p = new  person (); // 7  8  person (); //  

Similarly, change the way you declare a variable from Var to this, as follows:

1 function Person () {2   this. Name = ' Tom '; 3   return ' Jack '; 4 }56varnew person ();         // P  person{name: ' Jack '}  similarly 7 person ();                     // "Jack"                    

Return a worthwhile type is a reference type (Object, Array, Function):

1 functionPerson () {2    This. Name = ' Tom ';3   return{name: ' Jack '};4 }5 6 varp =NewPerson ();//P object{name: ' Jack '};7P.name;//' Jack '8Person ();//object{name: ' Jack '}9 Ten //thus, when the return value type of a function is a reference type, the new operator is equivalent to the result of a direct call;

JavaScript functions call regular calls and are called with new