JavaScript has many different
operators, which come in several
flavors, including binary. This
tutorial will cover some of the
most essential assignment,
comparison, arithmetic and logical
operators.
Selected assignment operators
An assignment operator assigns
a value to its left operand based
on the value of its right operand.
The basic assignment operator is
equal (=), which assigns the value
of its right operand to its left
operand. The other operators are
shorthand for standard operations.
Find an abridged list of shorthand
operators below:
| Shorthand operator |
Meaning |
| x += y |
x = x + y |
| x -= y |
x = x - y |
| x *= y |
x = x * y |
| x /= y |
x = x / y |
Note that the = sign here
refers to assignment, not "equals"
in the mathematical sense. So if x
is 5 and y is 7, x = x + y is not
a valid mathematical expression,
but it works in JavaScript. It
makes x the value of x + y (12 in
this case).
EXAMPLES: If
x = 10 and y = 2, x += y would
mean x = x + y, hence x's new
value would be the sum of x's
previous value plus y's previous
value. Upon executing x = x + y =
10 + 2, x's new value becomes 12,
while y's new value remains equal
to its old value. Similarly, x -=
y would change x's value to 8.
Calculate x *= y and x /= y to get
a better idea of how these
operators work.
Comparison operators
A comparison operator compares
its operands and returns a logical
value based on whether the
comparison is true or not. The
operands can be numerical or
string values. When used on string
values, the comparisons are based
on the standard lexicographical
ordering. They are described in
the following table.
| Operator |
Description |
Example |
| Equal (= =) |
Evaluates to true if the
operands are equal. |
x == y evaluates to true
if x equals y. |
| Not equal (!=) |
Evaluates to true if the
operands are not equal. |
x != y evaluates to true
if x is not equal to y. |
| Greater than
(>) |
Evaluates to true if left
operand is greater than right
operand. |
x > y evaluates to true if
x is greater than y. |
| Greater than
or equal (>=) |
Evaluates to true if left
operand is greater than or
equal to right operand. |
x >= y evaluates to true
if x is greater than or equal
to y. |
| Less than (<) |
Evaluates to true if left
operand is less than right
operand. |
x < y evaluates to true if
x is less than y. |
| Less than or
equal (<=) |
Evaluates to true if left
operand is less than or equal
to right operand. |
x <= y evaluates to true
if x is less than or equal to
y. |
EXAMPLES: 5
== 5 would return TRUE. 5 != 5
would return FALSE. (The statement
'Five is not equal to five.' is
patently false.) 5 <= 5 would
return TRUE. (Five is less than or
equal to five. More precisely,
it's exactly equal to five, but
JavaScript could care less about
boring details like that.)
Selected Arithmetic Operators
Arithmetic operators take
numerical values (either literals
or variables) as their operands
and return a single numerical
value. The standard arithmetic
operators are addition (+),
subtraction (-), multiplication
(*), division (/) and remainder
(%). These operators work as they
do in other programming languages,
as well as in standard algebra.
Since programmers frequently
need to add or subtract 1 from a
variable, JavaScript has shortcuts
for doing this. myVar++ adds one
to the value of myVar, while myVar--
subtracts one from myVar.
EXAMPLES: Let
x = 3. x++ bumps x up to 4, while
x-- makes x equal to 2.
Logical Operators
Logical operators take Boolean
(logical) values as operands and
return a Boolean value. That is,
they evaluate whether each
subexpression within a Boolean
expression is true or false, and
then execute the operation on the
respective truth values. Consider
the following table:
| Operator |
Usage |
Description |
| and (&&) |
expr1 && expr2 |
True if both logical
expressions expr1 and expr2
are true. False otherwise. |
| or (||) |
expr1 || expr2 |
True if either logical
expression expr1 or expr2 is
true. False if both expr1 and
expr2 are false. |
| not (!) |
!expr |
False if expr is true;
true if expr is false. |
EXAMPLES: Since
we have now learned to use the
essential operators, we can use
them in conjunction with one
another. See if you can work out
why the following examples resolve
the way they do:
If x = 4 and y = 7, ((x + y +
2) == 13) && (((x + y) / 2) == 2)
returns FALSE.
If x = 4 and y = 7, ((y - x +
9) == 12) || ((x * y) == 2)
returns TRUE.
If x = 4 and y = 7, !((x/2 + y)
== 9) || ((x * (y/2)) == 2)
returns FALSE.
