closure_functions.js

//Foo is in the global namespace.  Let's see which closure contents overwrite it.
foo = function() { console.log("FOO"); };

// Defining a named function will never overwrite the global namespace.
(function() {
   function foo() { console.log("OH NOES"); }
})();

foo(); //FOO

// Using a multi-line comma delimited list with a var declaration at the
// first item will not overwrite the global namespace.
(function() {

    var bar = function() { 
        console.log("BAR");
    },

    foo = function() {
        console.log("OH NOES");
    };
   
})();

foo(); //FOO

//However, it is simple to create a single typo (semicolon for comma) which will
//cause all following items to overwrite the global namespace.
(function() {

    var bar = function() { 
        console.log("BAR");
    };

    foo = function() { console.log("OH NOES"); }

})();

foo(); //OH NOES

//Let's reset the global foo before our next example.
function foo() { console.log("FOO"); }


//Here, we see that extraneous commas at the end of a standalone
//global variable declaration do not reliably[1] cause a syntax
//error, and so we will receive no warning that we're unintentionally
//polluting the global namespace.
(function() {

    var bar = function() { 
        console.log("BAR");
    };

    foo = function() { console.log("OH NOES"); },

    bizz = function() { console.log("BIZZ"); }

})();

foo(); //OH NOES

//[1] Internet Explorer will throw a syntax error on extraneous commas.