Booleans

A boolean is a data type which has two possible values: true or false.

Most programming languages have a concept of booleans.

Apart from the direct values of true and false, comparison operators also result in a boolean value.

For example for our if statements we have been comparing numbers.

5 < 10 results in the boolean value true

12 < 10 results in the boolean value false

The if statement expects a boolean value:

if (boolean) {
}

For example the following if statement will always execute:

if (true) {
}

The for loop also requires a boolean for its condition. Note that we use a comparison operator:

for (var i = 0; i < 10; i++) {
}

The following for loop will loop forever:

for (var i = 0; true; i++) {
}

A for loop will only end when its condition becomes false, this for loop will never execute its body because it always checks the condition before executing the body:

for (var i = 0; false; i++) {
}

The order of execution for for loops is:

1. Initialisation (e.g. var i = 0)
2. Condition (e.g. i < 10)
3. Execute the body
4. Increment (e.g. i++)