Logical Operators

Here’s the logical expression used to represent Julia’s weekend plans:

var colt = "not busy";
var weather = "nice";

if (colt === "not busy" && weather === "nice") {
  console.log("go to the park");
}

Prints: "go to the park"

Notice the && in the code above.

The && symbol is the logical AND operator, and it is used to combine two logical expressions into one larger logical expression. If both smaller expressions are true, then the entire expression evaluates to true. If either one of the smaller expressions is false, then the whole logical expression is false.

Another way to think about it is when the && operator is placed between the two statements, the code literally reads, "if Colt is not busy AND the weather is nice, then go to the park".

Logical expressions

Logical expressions are similar to mathematical expressions, except logical expressions evaluate to either true or false.

11 != 12

Returns: true

You’ve already seen logical expressions when you write comparisons. A comparison is just a simple logical expression.

Similar to mathematical expressions that use +, -, *, / and %, there are logical operators &&, || and ! that you can use to create more complex logical expressions.

Logical operators

Logical operators can be used in conjunction with boolean values (true and false) to create complex logical expressions.

By combining two boolean values together with a logical operator, you create a logical expression that returns another boolean value. Here’s a table describing the different logical operators:

Operator	Meaning	Example	How it works
`&&`	Logical AND	`value1 && value2`	Returns `true` if both `value1` and `value2` evaluate to `true`.
`\|\|`	Logical OR	`value1 \|\| value2`	Returns `true` if either `value1` or `value2` (or even both!) evaluates to `true`.
`!`	Logical NOT	`!value1`	Returns the opposite of `value1`. If `value1` is `true`, then `!value1` is `false`.

By using logical operators, you can create more complex conditionals like Julia’s weekend example.

Using Logical Operators

INSTRUCTOR NOTE:

Logical operators can be used to combine multiple conditional statements into a single statement.

TIP: Logical expressions are evaluated from left to right. Similar to mathematical expressions, logical expressions can also use parentheses to signify parts of the expression that should be evaluated first.

Logical Expression 1

What value of [BLANK] would make the following expression evaluate to false. Notice the ! right at the beginning!

!([BLANK] === 4) && "STRing" === "STRing"

Returns: false

-4

4

"4"

"-4"

SOLUTION:

`4`

Logical Expression 2

Select the operator that would make the following expression evaluate to true.

3 < -10 [BLANK] "James" !== "james"

Returns: true

!

||

&&

SOLUTION:

`||`

More Complex Logical Expressions

SOLUTION:

`true || false`
`(13 > -7) || (false == 0)`
`(3 != 6 % 3) && !(24 > 45) && (!false)`