not identically equal operator : Relational Operators « Operators « JavaScript Tutorial

The not identically equal operator is represented by an exclamation point followed by two equal signs (!==) and returns true only if the operands are not equal without conversion.

var sNum = "55";
var iNum = 55;
alert(sNum != iNum);    //outputs "false"
alert(sNum !== iNum);   //outputs "true"

2.9.Relational Operators
2.9.1.Equal and Not Equal
2.9.2.Equal Operator
2.9.3.A Comparison Operator returns boolean variable
2.9.4.!= (Not Equal)
2.9.5.Identically Equal and Not Identically Equal
2.9.6.not identically equal operator
2.9.7.!== (Non-Identity)
2.9.8.< (Less Than)
2.9.10.> (Greater Than)
2.9.11.>= (Greater Than or Equal)