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. You 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
=== for comparison.
<=less than or equal to
>=greater than or equal to
!==not equal to
A tiny note: for equality and inequality, there are also
!=, 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,
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
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; console.log(isInfant(3));
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? 😶
If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:
- Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
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.
In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.
I've read the lessons but nothing is clear 🙄
It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.
By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.
Logical type (boolean) a data type with two possible values: true and false.