tips and tricks.txt

1 – Don’t forget var keyword when assigning a variable’s value for the first time.

Assignment to an undeclared variable automatically results in a global variable being created. Avoid global variables.

2 – 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 

3 – undefined, null, 0, false, NaN, '' (empty string) are all falsy.

4 – Use Semicolons for line termination :
The use of semi-colons for line termination is a good practice. You won’t be warned if you forget it,
because in most cases it will be inserted by the JavaScript parser. 

5 – Create an object constructor

function Person(firstName, lastName){
    this.firstName =  firstName;
    this.lastName = lastName;        
}  

var Saad = new Person("Saad", "Mousliki");

7 – 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)


8 – 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)];

31 – Serialization and deserialization (working with JSON)

var person = {name :'Saad', age : 26, department : {ID : 15, name : "R&D"} }; 
var stringFromPerson = JSON.stringify(person); 
/* stringFromPerson is equal to "{"name":"Saad","age":26,"department":{"ID":15,"name":"R&D"}}"   */ 
var personFromString = JSON.parse(stringFromPerson);  
/* personFromString is equal to person object  */

32 – Avoid the use of eval() or the Function constructor

Use of eval or the Function constructor are expensive operations as each time they are called script engine must convert source code to executable code.

var func1 = new Function(functionCode);
var func2 = eval(functionCode);


35 – Pass functions, not strings, to setTimeout() and setInterval()

If you pass a string into setTimeout() or setInterval(), the string will be evaluated the same way as with eval, which is slow. Instead of using…

setInterval('doSomethingPeriodically()', 1000);  
setTimeout('doSomethingAfterFiveSeconds()', 5000);
…use…

setInterval(doSomethingPeriodically, 1000);  
setTimeout(doSomethingAfterFiveSeconds, 5000);