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JavaScript: Boolean type

As well as arithmetic operators, we also know comparison operators from school. For example, 5 > 4. It sounds like a question, "Is 5 greater than 4?" The answer is "yes". In other cases, the answer may be "no", say, for 3 < 1.

Comparison operators aren't restricted to numbers. YYou can put them in almost anything, e.g., strings. Every time we visit a website, it compares the username and password we've entered with those in the database. If they exist, we are let in (authorized).

Programming languages have borrowed all the comparison operators from math virtually unchanged. The only major change concerns the equality and inequality operators. In math, the usual equal sign is =, which is rare in programming. In many languages, the symbol = is used to assign values to variables, so you need to use == or === for comparison.

List of comparison operators in JavaScript:

  • < less than
  • <= less than or equal to
  • > greater than
  • >= greater than or equal to
  • === equal to
  • !== not equal to

A tiny note: for equality and inequality, there are also == and !=, neither of which we'll use because of the possible risks. We'll discuss it later.

A logical operation like 5 > 4 or password === text is an expression resulting in a special value, true or false. This is a new data type for us, which is called boolean. It has only these two values.

const result = 5 > 4;
console.log(result); // => true
console.log('one' !== 'one'); // => false

Along with strings and integers with rationals (which are numbers), the logical type (boolean) is one of JavaScript's primitive data types.

Try to write a primitive function that takes a child's age as an input and decides whether they are an infant or not. Infants are defined as children under a year old:

const isInfant = (age) => age < 1;

We can take advantage of the fact that any operation is an expression, so the only line we need to write here is "return the value that results from age < 1".

Depending on the input, the comparison will either be true or false, and return will return that result.

const isInfant = (age) => age < 1;


Now, perform the check on a child who is six months old:



Write a function, isPensioner(), which takes one parameter (a person's age), and check whether that person is retired or not. A pensioner is a person who has reached the age of 60 or higher.


isPensioner(75); // true
isPensioner(18); // false
The exercise doesn't pass checking. What to do? 😶

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In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

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I've read the lessons but nothing is clear 🙄

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  • Logical type (boolean) - a data type with two possible values: true and false.

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