JavaScript: else

Let's write a function getTypeOfSentence() that analyzes text and returns a description of its tone: for ordinary sentences – General sentence, for interrogative ones – Question sentence.

getTypeOfSentence('Hodor');  // General sentence
  getTypeOfSentence('Hodor?'); // Question sentence

The function implementation:

const getTypeOfSentence = (sentence) => {
  // Declare a variable to store the sentence type
  let sentenceType;
  // A predicate that checks the end of the text
  // If it ends with the '?' character, it returns true,
  // otherwise false
  if (sentence.endsWith('?')) {
    // If the condition above was met,
    // then this is an interrogative sentence.
    // Assign the corresponding value to sentenceType.
    sentenceType = 'Question';
  } else {
    // In all other cases the sentence is a general one
    sentenceType = 'General';
  }

  // Using interpolation we build a string
  return `${sentenceType} sentence`;
};

We added the keyword else and a new block with curly braces. This block runs only if the condition in if is false.

┌───────────┐
      │ condition?│
      └─────┬─────┘
  true │         │ false
      ↓         ↓
┌──────────┐ ┌──────────┐
│ if body  │ │ else body│
└──────────┘ └──────────┘

Nested conditions

Inside the else block (just like inside the if block) you can nest other conditions. Thanks to the curly braces, the nesting is always explicitly visible:

const number = 10;

if (number > 10) {
  console.log('Number is greater than 10');
} else {
  if (number === 10) {
    console.log('Number is exactly 10');
  } else {
    console.log('Number is less than 10');
  }
}
// => Number is exactly 10

Here number > 10 is checked first. The condition is false, so control passes to else, where the nested condition number === 10 is checked. It is true — Number is exactly 10 is printed.

There are two ways to lay out an if-else construct. Using negation, you can swap the order of the blocks:

const getTypeOfSentence = (sentence) => {
  let sentenceType;
  // A negation was added
  // The contents of else moved to if and vice versa
  if (!sentence.endsWith('?')) {
    sentenceType = 'General';
  } else {
    sentenceType = 'Question';
  }

  return `${sentenceType} sentence`;
};

Which way is preferable? The human brain finds it easier to think in a straightforward way rather than through negation. Try to choose a check that does not contain negations, and adjust the contents of the blocks to fit it.

Instructions

Write a function normalizeUrl(url) that takes a string with a website address and returns a URL with the https:// protocol.

If the string already starts with https:// — return it as is. If it does not start with it — add https:// at the beginning.

normalizeUrl('https://hexlet.io'); // => 'https://hexlet.io'
normalizeUrl('hexlet.io');         // => 'https://hexlet.io'

Коммерческий опыт и Трудоустройство

Tips

if...else

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 🤨

My code is different from the teacher's one 🤔

I've read the lessons but nothing is clear 🙄

Прочитал урок — ничего не понятно 🙄

Found a bug? Have something to add? Pull requests are welcome!

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Your exercise will be checked with these tests:

import { expect, test } from 'vitest';
import f from './index.js';

test('test', () => {
  expect(f('yandex.ru')).toBe('https://yandex.ru');
  expect(f('https://yandex.ru')).toBe('https://yandex.ru');
});

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Teacher's solution will be available in:

20:00

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