JavaScript Tips and Best Practices-1

use === instead of ==

The == (or !=) operator performs an automatic type conversion if needed. The === (or !==) operator will not perform any conversion. It compares the value and the type, which could be considered faster than ==.

[10] === 10    // is false
[10]  == 10    // is true
'10' == 10     // is true
'10' === 10    // is false
 []   == 0     // is true
 [] ===  0     // is false
 '' == false   // is true but true == "a" is false
 '' ===   false // is false 

Be careful when using typeof, instanceof and constructor.

typeof : a JavaScript unary operator used to return a string that represents the primitive type of a variable, don’t forget that typeof null will return “object”, and for the majority of object types (Array, Date, and others) will return also “object”.
constructor : is a property of the internal prototype property, which could be overridden by code.
instanceof : is another JavaScript operator that check in all the prototypes chain the constructor it returns true if it’s found and false if not.

var arr = ["a", "b", "c"];
typeof arr;   // return "object" 
arr  instanceof Array // true
arr.constructor();  //[]

Create a Self-calling Function

This is often called a Self-Invoked Anonymous Function or Immediately Invoked Function Expression (IIFE). It is a function that executes automatically when you create it, and has the following form:

(function(){
    // some private code that will be executed automatically
})();  
(function(a,b){
    var result = a+b;
    return result;
})(10,20)

Get a random item from an array

var items = [12, 548 , 'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' , 2145 , 119];

var  randomItem = items[Math.floor(Math.random() * items.length)];

Don’t use delete to remove an item from array

Use splice instead of using delete to delete an item from an array. Using delete replaces the item with undefined instead of removing it from the array.

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ]; 
items.length; // return 11 
delete items[3]; // return true 
items.length; // return 11 
/* items will be equal to [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154,       119]   */