problems and pitfalls with the abstract equality operator, I recommend Douglas
Crockford’s book,
(O’Reilly).
Most of the problematic behavior of the abstract equality operators
surrounds the values null, undefined, the empty string, and the
number 0. For the most part, if you are comparing values that you
know not to be one of these values, it’s generally safe to use the
abstract equality operator. However, don’t underestimate the power
of rote habit. If you decide, as I recommend, to use the strict equal‐
ity operator by default, then you never have to think about it. You
don’t have to interrupt your thought flow to wonder whether it’s
safe or advantageous to use the abstract equality operator; you just
use the strict equality operator and move on. If you later find that
the strict equality operator isn’t producing the right result, you can
do the appropriate type conversion instead of switching to the
problematic abstract equality operator. Programming is hard
enough: do yourself a favor, and avoid the problematic abstract
equality operator.
Here are some examples of strict and abstract equality operators in use. Note that
even though objects
a
and
b
contain the same information, they are distinct objects,
and are neither strictly or abstractly equal:
const
n
=
5
;
const
s
=
"5"
;
n
===
s
;
// false -- different types
n
!==
s
;
// true
n
===
Number
(
s
);
// true -- "5" converted to numeric 5
n
!==
Number
(
s
);
// false
n
==
s
;
// true; not recommended
n
!=
s
;
// false; not recommended
const
a
=
{
name
:
"an object"
};
const
b
=
{
name
:
"an object"
};
a
===
b
;
// false -- distinct objects
a
!==
b
;
// true
a
==
b
;
// false; not recommended
a
!=
b
;
// true; not recommended
Relational operators compare values in relation to one another, and they only make
sense for data types that have a natural ordering, such as strings (“a” comes before
“b”) and numbers (0 comes before 1). The relational operators are less than (
<
), less
than or equal to (
<=
), greater than (
>
), and greater than or equal to (
>=
):
3
>
5
;
// false
3
>=
5
;
// false
3
<
5
;
// true
3
<=
5
;
// true
86 | Chapter 5: Expressions and Operators
