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JavaScript: Conditionals (`if`)

Conditional statements control the program's behavior depending on the conditions we want to test. They allow us to write complex programs that behave differently depending on the situation.

Consider a function to which we can pass a sentence and determine what type of sentence it is. To begin with, it will distinguish between normal sentences and question sentences.

const getTypeOfSentence = (sentence) => {
  const lastChar = sentence[sentence.length - 1];
  if (lastChar === '?') {
    return 'question';

  return 'general';

getTypeOfSentence('Hodor');  // general
getTypeOfSentence('Hodor?'); // question

if is a construct that controls the procedure by which statements are executed. You need to pass predicate expression to it in parentheses and then define a block of code in curly brackets. This code block executes only if the predicate is true.

If the predicate is false, we skip the code block in curly brackets, and the function keeps executing. Here, the next line of code, return 'general';, causes the function to return a string and terminate.

As you can see, return can be anywhere in a function. Including the interior of a conditional code block.

If the curly brackets after if contains only one line of code, you can leave out the brackets:

const getTypeOfSentence = (sentence) => {
  const lastChar = sentence[sentence.length - 1];
  if (lastChar === '?')
    return 'question';

  return 'general';

console.log(getTypeOfSentence('Hodor'));  // => general
console.log(getTypeOfSentence('Hodor?')); // => question

We advise against it and to always use curly brackets. That way you can clearly see where the conditional's body starts and ends. The code becomes clearer and more readable.


Write the guessNumber() function that takes a number and checks if it's equal to a given number (say, for example, 42). If it's equal, the function should return the string You win!'; otherwise, it should return the string 'Try again!'.

guessNumber(42) # 'You win!'
guessNumber(61) # 'Try again!'
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.

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