Javascript using Globals

Using Javascript Globals.

  • Javascript has a predefined global object, which serves as a placeholder for the global properties and global functions.
  • All the Javascript build-in objects such as Object, Number, String and Date are considered as global properties.
  • Functions and variables that you define outside of a function or object of any kind is to be regarded as a global property.

    function print(str){     // 'print' is a global function
        document.write(str+"<br>");
      }
      var mystr="Hello"; // 'mystr' is a global string
  • The global object has no name, but if your host environment is the web browser, the global object is called window.
  • You can also on the top-level of Javascript use the this keyword as a reference to the global object.
  • You cannot create new global object, as there is no Global constructor function.
  • All pre-defined properties in the global object is non-enumerable in the core of Java Script. All of the other global properties (global variables) allows you to list with a for / in loop like this:

    <script type="text/javascript">
    var variables = ""
    for(var propname in this){
        variables += propname+" is typeof "+typeof this[propname] + "<br>";
    }
    document.write(variables+"<br>");
    </script>
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