One common mistake that I see developers do is exposing a variable to the Global object in chain assignment.
first I let’s see how can you expose a variable to the Global object by accident.
 
function test(){
a =12; // var is missing
return a;
}
test();
 
By missing the keyword var even though variable a is inside of the function but [...]

I have implemented a jQuery plugin that will take care of namespacing for us.
if you don’t know what is namespace please read it from here
take a look at the code below. and see how it works. you can get the code from jsfiddle as well
$.namespace("liteframe.actions.controller");
//OR [...]

If you are trying to remove elements from an array. and do not care what those elements are, you shouldn’t use array slice, array splice.
however there is an easier way of doing this.
by just changin the length of an array we can modify our array and remove items from it.
 
var arr = [1,2,3,4,5];
arr.length = 2;
console.log( [...]

Even though it is not recommended to use Array constructor. but sometimes we can get some usage of it.
One good example would be repeating a string without using a for loop.
in this example we are creating an empty array with default undefined values.
( when you specify a size for an array, without setting the values [...]

Sometimes some bad programmer or some hacker messes up with the undefined global variable in javascript.
so why would we really care about it.
the following are some examples that the variable undefined will be returned
 
 
var myVar = undefined; //Anything that has been set to the value of undefined.
 
function test(){}; console.log( test() ); // returns undefined – [...]