JavaScript: String comparison

Comparison operations work not only with numbers but also with strings. In JavaScript, strings are compared lexicographically: character by character from left to right by the numeric codes of the characters (Unicode).

console.log('apple' < 'banana'); // => true
console.log('cat' > 'dog');      // => false
console.log('abc' === 'abc');    // => true
console.log('hello' !== 'world'); // => true

Here 'apple' < 'banana', because the code of the character a (97) is less than the code of b (98), and it is the first differing character that decides the outcome of the comparison. You can find out the code of a character with the charCodeAt() method:

console.log('a'.charCodeAt(0)); // => 97
console.log('b'.charCodeAt(0)); // => 98

The comparison is case-sensitive: the code of 'Z' (90) is less than the code of 'a' (97). Here are a few examples where the first letters are in different cases:

console.log('Zebra' < 'apple');  // => true  — 'Z'(90) < 'a'(97)
console.log('apple' < 'Banana'); // => false — 'a'(97) > 'B'(66)
console.log('Apple' < 'apple');  // => true  — 'A'(65) < 'a'(97)

Let's write a function that checks whether a word starts with a given letter. To do this, we take the first character of the string and compare it with the required letter:

const startsWithLetter = (word, letter) => word[0] === letter;

console.log(startsWithLetter('apple', 'a'));  // => true
console.log(startsWithLetter('banana', 'a')); // => false

Comparison operations are expressions just like arithmetic ones. You can substitute ready-made values and other expressions into them, for example word[0] above. You can also use the .length property:

console.log('apple'.length > 3); // => true, because the length is 5
console.log('hi'.length > 3);    // => false, because the length is 2

First 'apple'.length is evaluated (resulting in the number 5), and then this number is compared with 3. That is, the operands of the expression are computed first, and then the comparison is performed.

Useful predicates

Strings in JavaScript have built-in predicate methods. They return true or false and help check various properties of a string:

console.log('hello'.startsWith('he')); // => true — the string starts with 'he'
console.log('hello'.endsWith('lo'));   // => true — the string ends with 'lo'
console.log('hello'.includes('ell'));  // => true — the string contains 'ell'

Such methods let you check strings against the required conditions right in the code, without writing additional functions.

During registration on a website, the program checks that the password is long enough — more than 5 characters. Write a function isLongWord() that returns true if the length of the passed word is more than 5 characters, and false otherwise.

Example usage:

isLongWord('apple');  // => false
isLongWord('banana'); // => true