|ECMAScript Edition||ECMAScript 1st Edition includes all comparison operators except
ECMAScript 3rd Edition adds
===) is only true if the operands are the same Type. The more commonly used abstract comparison (e.g.,
==) converts the operands to the same Type before making the comparison. For relational abstract comparisons (e.g.,
<=), the operands are first converted to primitives, then the same Type, before comparison.
Strings are compared based on standard lexicographical ordering, using Unicode values.
Features of comparisons:
- Two strings are strictly equal when they have the same sequence of characters, same length, and same characters in corresponding positions.
- Two numbers are strictly equal when they are numerically equal (have the same number value). NaN is not equal to anything, including NaN. Positive and negative zeros are equal to one another.
- Two Boolean operands are strictly equal if both are
trueor both are
- Two distinct objects are never equal for either strictly or abstract comparisons.
- An expression comparing Objects is only true if the operands reference the same Object.
- Null and Undefined Types are
The following table describes the comparison operators:
|Operator||Description||Examples returning true1|
|Not equal (
|Strict equal (
||Returns true if the operands are strictly equal (see above) with no type conversion.||
|Strict not equal (
||Returns true if the operands are not equal and/or not of the same type.||
|Greater than (
||Returns true if the left operand is greater than the right operand.||
|Greater than or equal (
||Returns true if the left operand is greater than or equal to the right operand.||
|Less than (
||Returns true if the left operand is less than the right operand.||
|Less than or equal to (
||Returns true if the left operand is less than or equal to the right operand.||
1 These examples assume that
var1 has been assigned the value 3 and
var2 has been assigned the value 4.
Using the Equality Operators
The standard equality operators (
!=) use the Abstract Equality Comparison Algorithm to compare two operands. If the operands are of different Types, it will attempt to convert them to the same Type before making the comparison, e.g., in the expression
5 == '5', the string on the right is converted to Number before the comparison is made.
The strict equality operators (
!==) use the Strict Equality Comparison Algorithm and are intended for performing equality comparisons on operands of the same Type. If the operands are of different Types, the result is always
5 !== '5'.
Use strict equality operators if the operands must be of a specific Type as well as value or if the exact Type of the operands is important. Otherwise, use the standard equality operators, which allow you to compare the identity of two operands even if they are not of the same Type.
Numbertype value. First, a mathematical value is derived from the string numeric literal. Next, this value is rounded to nearest
- If one of the operands is
Boolean, the Boolean operand is converted to 1 if it is
trueand +0 if it is
Numbervalue, using the
toStringmethods of the objects. If this attempt to convert the object fails, a runtime error is generated.
- Note that an object is converted into a primitive if, and only if, its comparand is a primitive. If both operands are objects, they're compared as objects, and the equality test is true only if both refer the same object.
'foo' === 'foo' // true as both operands are Type String (i.e. string primitives) var a = new String('foo'); var b = new String('foo'); a == b // false as a and b are Type Object
and reference different objects a === b // false as a and b are Type Object and reference different objects a == 'foo' // true as a and 'foo' are of different type and, the Object (a) is converted to String 'foo' before comparison