A value that's either true
or false
.
Boolean
values help to make decisions in code. They appear any time a logical condition is checked. For example, the condition "Is a mouse button being pressed?" must be either true
or false
:
// If the user presses the mouse, draw a circle at
// the mouse's location.
if (mouseIsPressed === true) {
circle(mouseX, mouseY, 20);
}
The if
statement checks whether mouseIsPressed is true
and draws a circle if it is. Boolean
expressions such as mouseIsPressed === true
evaluate to one of the two possible Boolean
values: true
or false
.
The ===
operator (EQUAL) checks whether two values are equal. If they are, the expression evaluates to true
. Otherwise, it evaluates to false
.
Note: There's also a ==
operator with two =
instead of three. Don't use it.
The mouseIsPressed system variable is always true
or false
, so the code snippet above could also be written as follows:
if (mouseIsPressed) {
circle(mouseX, mouseY, 20);
}
The !==
operator (NOT EQUAL) checks whether two values are not equal, as in the following example:
if (2 + 2 !== 4) {
text('War is peace.', 50, 50);
}
Starting from the left, the arithmetic expression 2 + 2
produces the value 4
. The Boolean
expression 4 !== 4
evaluates to false
because 4
is equal to itself. As a result, the if
statement's body is skipped.
Note: There's also a !=
operator with one =
instead of two. Don't use it.
The Boolean
operator &&
(AND) checks whether two expressions are both true
:
if (keyIsPressed === true && key === 'p') {
text('You pressed the "p" key!', 50, 50);
}
If the user is pressing a key AND that key is 'p'
, then a message will display.
The Boolean
operator ||
(OR) checks whether at least one of two expressions is true
:
if (keyIsPressed === true || mouseIsPressed === true) {
text('You did something!', 50, 50);
}
If the user presses a key, or presses a mouse button, or both, then a message will display.
The following truth table summarizes a few common scenarios with &&
and ||
:
true && true // true
true && false // false
false && false // false
true || true // true
true || false // true
false || false // false
The relational operators >
, << code="">, <code>>=</code>, and <code><=< code=""> also produce <code>Boolean</code> values:<!--=<--></code><!--<-->
2 > 1 // true
2 < 1 // false
2 >= 2 // true
2 <= 2="" true="" <="" code=""/>
See if for more information about if
statements and Number for more information about Number
s.
Examples
Related References
stringify
From the MDN entry: The JSON.stringify() method converts a JavaScript object or value to a JSON string.
log
Prints a message to your browser's web console.
===
The strict equality operator === checks to see if two values are equal and of the same type.
Array
A list that keeps several pieces of data in order.