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.

Instructions

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!'