The Modified Equality Operators in Javascript

JavaScript 1.3 changes the way equality operators work, revertingback to JavaScript 1.1's rules. JavaScript 1.2 handles standardequality operators the same way JavaScript 1.3 handles strict equalityoperators (see previous page). When the operators are of differenttypes, JavaScript 1.2 does not attempt to do any type conversion tohelp the comparison -- it always returns falsewhen the operands are of different types.

For example, the following standardequality test:

if (5 == "5")

returns false in JavaScript 1.2, because 5 is a number and "5" is a string.

Since JavaScript 1.3 explicitly supports strict equality operators (=== and !==),it can be more relaxed in the standard equality operators and do a typeconversion before comparison, if necessary.

Conversion is applied onoperands of the type String, Number, Boolean, or Object.

The most common different-type-operand comparison is between anumber and a string. The string is converted to a number via anelaborate algorithm. First, it is converted to a mathematical value.Then it is rounded to the nearest Number type value, according to the Number type of the other operand. For example, JavaScript 1.3 will return true for the following test:

if (5.12 == "5.12e0")

When you compare a number and a Boolean, the Boolean operand is converted to 1 if it is true, and to 0 if it is false. The following test will yield true:

if (1 == true)

as well as this one:

if (0 == false)

When you compare an Object with a Number, JavaScript 1.3 converts the Object to a Number by the valueOf() method. When you compare an Object with a String, JavaScript 1.3 converts the Object to a String by the toString() method. Referring to our previous assembly line example, the following test will yield true:

if ("[object Object]" == volvoInterior)