javascript equality operator

Equal (==) 

Not equal (!=)

Strict equal (===)
Strict not equal (!==)

Greater than (>)

Greater than or equal (>=)

Less than (<)

Less than or equal to (<=)

You can also check the equality like ..

'' == '0'           // false
0 == ''             // true
0 == '0'            // true

false == 'false'    // false
false == '0'        // true

false == undefined  // false
false == null       // false
null == undefined   // true

' \t\r\n ' == 0     // true

"variable=== undefined". If you want to check if a variable contains data use 

"if (variable)"

This is the same as 
"if (variable !== undefined && variable !== null)"
You should always use === instead of ==

With == you are implicitly doing a type conversion, e.g. 1 == "1" = true, 1 === "1" = false.