We've already seen how we can use the
= operator to set a variable equal to a value.
> const favoriteNumber = 42; > favoriteNumber; 42
= is called an assignment operator because it assigns the value on the right of the operator to the variable on the left. In the above example,
favoriteNumber is assigned the value 42.
Another assignment operator is the
+= operator, because it too assigns a new value to the variable on the left based on the value to the right.
> let myNumber = 5; > myNumber += 1; > myNumber; 6
There is an assignment operator for each of the mathematical functions: addition, subtraction, multiplication and division.
+= -= *= /=
When you use any of these assignment operators, the value of the variable on the left side is changed by the math operation and value on the right. Let's do one of each:
> let testNumber = 10; > testNumber += 5; > testNumber; 15 > testNumber -= 9; > testNumber; 6 > testNumber *= 3; > testNumber; 18 > testNumber /= 2 > testNumber; 9
Visit this link to MDN to for reference pages on assignment operators:
Assignment operators change the value of the variable on the left of the operator. Comparison operators do not change any values, but return
> const myNumber = 5; > myNumber < 10; true > myNumber > 10; false
Comparison operators are also called relational operators, because they help find the relationship between two operands, asking questions like, "is 10 bigger than 5?", or
10 > 5.
>Greater Than Operator
> means "greater-than (and not equal to)":
3 > 4evaluates to
3 > 3also evaluates to
false, because 3 is equal to 3 and not greater.
3 > 2evaluates to
<Less Than Operator
< is the opposite of
>. It means "less-than (and not equal to)":
3 < 5evaluates to
3 < 3evaluates to
falsebecause they are equal.
>=Greater Than or Equal Operator
>= is the same as
>, except it evaluates to
true if the two sides are equal:
3 >= 3evaluates to
3 >= 2also evaluates to
<=Less Than or Equal Operator
<= is the opposite of
>=. It means "less-than-or-equal-to":
3 <= 3evaluates to
truebecause 3 is equal to 3.
3 <= 1evaluates to
3 <= 5evaluates to
In the above examples, notice that the comparison operators return one of two values:
false. Notice that there are no quotes around these values.
false aren't strings - they're called booleans. They simply represent being true or false.
Visit this link to MDN to for reference pages on relational operators:
We can also compare the equality of two operands with equality operators. This means we can check to see whether or not two operands have the same value. Equality operators also only return the booleans
> const myNumber = 5; > myNumber === 10; false > myNumber === 5; true
Notice the triple equals operator,
===. This is a type of equality operator. When we're asking whether something is equal, we use
=== (3 equal signs). When we're setting a variable equal to something, we use
= (single equal sign). Mixing these up is one of the easiest syntax errors to make.
==, but it is almost never used, and you should generally avoid it. It does things like return
true for equality comparisons of
"2" == 2 (indicating that a number and a string are the same!), and many of its rules are confusing, inconsistent, and hard to remember. If you want to read about the double equals operator, visit this MDN documentation.
We can also check the opposite of equality - not being equal - with the inequality operator
> const myNumber = 5; > myNumber !== 10; true > myNumber === 5; false
Equality operators work for strings as well.
> const greeting = "hello world"; > greeting === "hello world"; true > greeting === "goodbye"; false > greeting; "hello world"
Notice that if you type
greeting after using the equality operators, you will see that the variable
greeting still contains the string
"hello world". Comparison and equality operators do not change the value of the variable. Let's look at another example to illustrate that important difference between assignment operators and comparison/equality operators.
> let myNumber = 5; > myNumber === 5; true > myNumber === 10; false > myNumber = 10; > myNumber === 10; true > myNumber === 5; false
Note that we use
let instead of
const here because we reassign the value of
myNumber = 10. We wouldn't be able to do that if
myNumber were a constant variable declared with
Here are some more examples of equality operators.
--- means "equal-to".
5 === 5or
"cat" === "cat"evaluate to
3 === 5or
"cat" === "dog"evaluate to
!== means "not-equal-to". It is the opposite of
"cat" !== "dog"evaluates to
5 !== 5evaluates to
false, because saying that 5 is not equal to 5 is not true.
Visit this link to MDN to for reference pages on equality operators:
false are booleans. They are not strings - they simply represent being true or false.
Assignment operator: Changes the value of the variable on the left of the operator.
Comparison operator: Does not change any values, but returns a boolean (
false) depending on whether the statement evaluates as true or false.
Be aware of the difference between the
= assignment operator and the
=== comparison operator.
=assign variable on left of operator value on right of operator
+=increase value of variable on left of operator by value on right of operator
-=decrease value of variable on left of operator by value on right of operator
*=multiply value of variable on left of operator by value on right of operator
/=divide value of variable on left of operator by value on right of operator
===is equal to
!==is not equal to
>=greater than or equal to
<=less than or equal to
Lesson 17 of 65
Last updated May 23, 2022