pxt-calliope/olddocs/js/boolean.md

Boolean

true or false.

@parent js/language

A Boolean has one of two possible values: true; false. Boolean (logical) operators (and, or, not) take Boolean inputs and yields a Boolean value. Comparison operators on other types (numbers, strings) yields a Boolean value.

Block Editor

In the Block Editor, the following blocks represent the true and false Boolean values, which can be plugged in anywhere a Boolean value is expected:

The next three blocks represent the three Boolean (logic) operators:

The next six blocks represent comparison operators that yield a Boolean value. Most comparisons you will do involve numbers:

Touch Develop

~hide

let condition = true
let condition2 = true

~

Boolean values and operators are often used with an if or while statement to determine which code will execute next. For example:

if (condition && condition2) {
    // This code runs if both `condition` and `condition2` are `true`
} else {
    // This code runs if either `condition` or `condition2` is `false`
}

Functions that return a Boolean

Some functions return a Boolean value, which you can store in a Boolean variable. For example, the following code gets the on/off state of point (1, 2) and stores this in the Boolean variable named on. Then the code clears the screen if on is true:

let on = led.point(1, 2)
if (on) {
    basic.clearScreen()
}

Boolean operators

Boolean operators take Boolean inputs and evaluate to a Boolean output:

Conjunction: A and B

A and B evaluates to true if-and-only-if both A and B are true:

• false and false = false

• false and true = false

• true and false = false

• true and true = true

Disjunction: A or B

A or B evaluates to true if-and-only-if either A is true or B is true:

• false or false = false

• false or true = true

• true or false = true

• true or true = true

Negation: not A

not A evaluates to the opposite (negation) of A:

• not false = true
• not true = false

Example

This example turns on LED 3 , 3, if LEDs 1 , 1 and 2 , 2 are both on:

if (led.point(1, 1) && led.point(2, 2)) {
    led.plot(3, 3)
}

Comparisons of numbers and strings

When you compare two Numbers, you get a Boolean value, such as the comparison x < 5 in the code below:

let x = Math.random(10)
if (x < 5) {
    basic.showString("Low", 150)
} else {
    basic.showString("High", 150)
}

See the documentation on Numbers for more information on comparing two Numbers. You can also compare strings using the equals function.

See also

if, while, number