如何在javascript中调用窗口对象的用户定义函数

Question

I am trying to call a function from outside which is defined with in a window object, but it throws an error.

    window.vcm = (function() {
    "use strict";
     function red(){
      alert('red');
     }   
   });  
  vcm.red();//Error at this line...

I am new to OOPS in javascript. Can somebody tell me how to call this function here.

Answer 1

The value that is vcm does not have a red property.

Perhaps you mean this instead, wherein vcm is an object that has a property red that is function you can call:

window.vcm = {
  red: function(){
    "use strict";
    alert('red');
  }   
};

It's also a possibility (albeit not somewhat you 'd see in practice) for vcm itself to be a function and for it to have a red property that is a function:

window.vcm = (function() {
  "use strict";
   var vcm = function() { alert("vcm"); }
   vcm.red = function() { alert('vcm.red'); };
   return vcm;
 })();

vcm();     // "vcm"
vcm.red(); // "vcm.red"

Answer 2

There are two approaches.

Approach 1 : window.vcm = { red: function (){ "use strict"; alert('red'); } }; vcm.red(); window.vcm = { red: function (){ "use strict"; alert('red'); } }; vcm.red();

Approach 2 :

window.vcm = (function() {
    "use strict";
   this.red = function(){
      alert('red');
    }   
});
var x = new vcm();
x.red(); 

Answer 3

red only exist inside the function you assigned to window.vcm and also only when the function is executed. Furthermore, functions don't have a property red .

Consider this simpler example:

function foo() {
    function bar() {}
}

bar(); // will throw an error

Calling bar will throw an error because bar is not defined in the scope where it is called.

It seems you want to assign an object to window.vcm , which has a property red :

window.vcm =  {
    red: function (){
        "use strict";
        alert('red');
    }
};

Here I am using an object literal to create an object with the property red .

More information:

• MDN - Working with objects