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Logical operators

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Decisions might require more than one comparison and can be strung together with logical operators to produce a Boolean value.

Logical operators and Booleans

There are specific operators that let us connect many Boolean statements. The result is a more complex statement that still evaluates to true or false. You can use the following set of operators to construct these more complex comparisons:

Symbol	Description	Example
&&	Logical AND: Compares two Boolean expressions. Returns true only if both sides are true.	(5 > 6) && (5 < 6 ) //One side is false, other is true. Returns false
||	Logical OR: Compares two Boolean expressions. Returns true if at least one side is true.	(5 > 6) || (5 < 6) //One side is false, other is true. Returns true
!	Logical NOT: Returns the opposite value of a Boolean expression.	!(5 > 6) // 5 is not greater than 6, but "!" will return true

Conditions and decisions with logical operators

You can use these complex operators with both assignments but also with if and else clauses.

In assignments

As part of assigning a value to a variable, you can use an or (||) operator.

let isHoliday = true;
let isMember = true;
let hasDiscount = isHoliday || isMember;

With the preceding code, you express whether a customer can have a discount or not. Only one of the variables, isMember or hasDiscount, needs to have a truthy value for the hasDiscount variable to be assigned true.

In if...else

You can also use this kind of logical operator in an if/else statement. In the following code example, you have a situation where there are two laptops, one on discount and one sold at full price. By using an || operator, you're able to construct a more complex-looking if clause.

let currentMoney= 800;
let laptopPrice = 1000;
let laptopDiscountPrice = laptopPrice - (laptopPrice * .20) //Laptop price at 20 percent off

if (currentMoney >= laptopPrice || currentMoney >= laptopDiscountPrice){
    //Condition was true. Code in this block will run.
    console.log("Getting a new laptop!");
}
else {
    //Condition was true. Code in this block will run.
    console.log("Can't afford a new laptop, yet!");
}

Tip

Remember what we said about learning to read code? What does the code tell you? Are you getting a new laptop? Scroll down for the answer.

Yes, you are.

Negation operator

You've seen how you can use an if...else statement to create conditional logic. Anything that goes into an if needs to evaluate to true or false. By using the ! operator, you can negate the expression. It would look like so:

if (!condition) {
  // runs if condition is false
} else {
  // runs if condition is true
}

Ternary expressions

Using if...else isn't the only way to express decision logic. You can also use something called a ternary operator. The syntax for it looks like this:

let variable = condition ? <return this if true> : <return this if false>

Here's a more tangible example:

let firstNumber = 20;
let secondNumber = 10
let biggestNumber = firstNumber > secondNumber ? firstNumber: secondNumber;

The code states that:

if firstNumber is larger than secondNumber, then assign firstNumber to biggestNumber, otherwise assign secondNumber.

Tip

Take a minute to read this code a few times. Do you understand how these operators are working?

The ternary expression is a compact way of writing the following code:

let biggestNumber;
if (firstNumber > secondNumber) {
  biggestNumber = firstNumber;
} else {
  biggestNumber = secondNumber;
}

Tip

Take a moment to reflect. Which of the two approaches, ternary expressions or if/else, was easier to understand?

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