JavaScript's understanding of semantic functions

See code Example 1

    　　　 varA=1; functionM (a) {//here is the parameter of the first incoming function of the formal parameter, both arguments[0]alert (a);//where a is bound to a formal parameter} m (a);//1 A In this case passes the variable a as a parameter to the function.......................................................................................................        varA=1; functionm (a) {alert (a); } m ();//Undefind is bound to a function as null because there are no parameters passed in, so alert a undefined

code Example 2

 var  a=1;  function  m () {//              alert (a);        alert (b);  function   n () { var  a=5;  var  b=3; //         m (); } n ();  //  alert A is 1, to the B-times wrong is not defined  m (); //  alert A is 1, to the B-times wrong is not defined  

The visible function m, when created, has bound itself to the scope of the creation environment, where it is a global scope, and when called in function N, it does not look for a variable in the private scope of function n, so the function n defines

A and B do not appear in the scope chain of the function m, as shown in the comments in the code.

code example 3

      var a=1;         function   m (a) {///A In this case and a in the function are formal parameters and have no relation to the a variable declared in the first line, they have no binding relationship in Instance 2            alert (a);        }         function N () {            var a=5;//             M (a);//The variable A is passed into function m, and when alert A is required, the value of a is alert,        }        N (); // 5        M (); // Undefind

Here the difference is due to the differentiated participation variable.

The scope of the anonymous function is more complex, wait for a good sleep and then get up and tidy up.

JavaScript's understanding of semantic functions