Operators

If you have been following this lessons in the order listed, we have already covered many operators. But here I’d like to cover operators a bit more in depth.

Expressions

As mentioned in a previous lesson, an expression is a unit of code that resolves to a value. To expand on this, and expression may have side effects such as assigning a value to a variable, or an expression may simply evaluate.

Regardless of the outcome, an expression will always have an operator and at least one operand.

Operators and Operands

Consider the following:

let x = 4;

x <= 5;

x = 4 + 5;

In the above, x, 4 and 5 are operands. The = and the <= are operators. The first expression is using the assignment operator (=) to assign the value of four to the variable x. The second expression is using a comparison operator (<=) which mean less than or equal to and this expression will resolve to true because 4 is in fact less than or equal to 5. The last expression is using both an assignment operator (=) and an arithmetic operator (+). The arithmetic operator will resolve the right hand side of the assignment operator to a value, that being 4 plus 5, or 9. The assignment operator then assigns the value 9 to the variable x.

All of the above operators are considered binary operators, which means that there is an operand on the left side, and operator in the middle, and a second operand on the right side. Even the last expression contains only binary operators, where the second operand relative to the assignment operator is itself a binary operation.

Expressions only one operand and one operator are known as unary operators. Examples include x++ or !x.

I will not comprehensively cover the operators of JavaScript, but the following is a table of the common operators, the type of operator they are, and a description.

Operator	Type	Description	Example
=	Assignment	The assignment operator assigns a value to a variable	x = 5
==	Comparison	The equality operator compares two values while performing coercion.	foo == "bar" x == 5 42 == "42"
!=	Comparison	Not equal, the inverse of the equality operator	x != 4
===	Comparison	Strict equality does not coerce the types of the values	foo === "bar" 4 === 4
!==	Comparison	Strict inequality, the inverse of strict equality	4 !== "4"
<	Comparison	Less than	4 < x
>	comparison	Greater than	6 > x
<=	Comparison	Less than or equal to	4 <= x
>=	comparison	Greater than or equal to	6 >= x
+	Arithmetic	Acts as arithmetic addition for numbers as well as concatination for strings	4 + 5 "hello" + " world"
-	Arithmetic	Subtraction	5 - 4
*	Arithmetic	Multiplication	5 * 4
/	Arithmetic	Division	5 / 4
%	Arithmetic	Modulo returns the remander of a division	4 % 2
**	Arithmetic	Exponent	x ** 2
++	Arithmetic	Increment by 1	x++ ++x
--	Arithmetic	Decrement by 1	x-- --x
&&	Logical	AND operator returns true if both operands evaluate to true	x == 5 && y < x
||	Logical	OR operator returns true if either or both operands evaluate to true	x == 5 || x == 3