Use === and !==

gistfile1.js

// Use === and !==

// It is often better to use the === and !== operators  
// rather than == and != operators. The reason for this
// is that === and !== (also known as the identity operators)
// check for the type as well as the value when being compared
// whereas the == and != will try to coerce the two values
// into the same type before the comparison is made, which
// may lead to some very unexpected results.

// Unexpected Comparisons using the == Operator
console.log( "\nUnexpected Comparisons using the == Operator" );
console.log( "0 ==  ''", 0 ==  '' );                     //true
console.log( "0 == '0'", 0 == '0' );                     //true
console.log( "false == '0'", false == '0' );             //true
console.log( "null == undefined", null == undefined );   //true
console.log( "' \t\r\n ' == 0", ' \t\r\n ' == 0 );       //true

// Expected Comparions using the === Operator
console.log( "\nExpected Comparions using the === Operator" );
console.log( "0 === ''", 0 === '' );                     //false
console.log( "0 === '0'", 0 === '0' );                   //false
console.log( "false === '0'", false === '0' );           //false
console.log( "null === undefined", null === undefined ); //false
console.log( "' \t\r\n ' === 0", ' \t\r\n ' === 0 );     //false​​​​​​​​