String Methods

Strings have many methods. These are the ones you will use most:

const word = "banana";

console.log(word.toUpperCase());
console.log(word.includes("an"));
console.log(word.startsWith("ba"));
console.log(word.endsWith("na"));
console.log(word.replaceAll("a", "o"));

Output:

BANANA
true
true
true
bonono

• toUpperCase() gives the string in capital letters. toLowerCase() does the opposite.
• includes(text) checks whether text appears anywhere in the string.
• startsWith and endsWith check the beginning and the end. fileName.endsWith(".csv") is a typical use.
• replaceAll(old, new) replaces every old with new.

There is also trim(), which removes spaces from both ends of a string. You cannot see spaces in the output, so this example prints the length before and after:

const padded = "  hi  ";
console.log(padded.length);
console.log(padded.trim().length);

Output:

6
2

One rule is true for all of these methods: strings cannot be changed. A method never changes the string you call it on. It returns a new string instead:

const s = "hello";
s.toUpperCase();
console.log(s);

const up = s.toUpperCase();
console.log(up);

Output:

hello
HELLO

The call on the second line made a new string, but nothing stored it, so it was lost. Always keep the result, in a variable or by printing it.

Be careful with replace. Without "All", it replaces only the first match:

console.log("banana".replace("a", "o"));
console.log("banana".replaceAll("a", "o"));

Output:

bonana
bonono

Searches and comparisons also care about capital letters. "banana".includes("An") is false. When you check what a user typed, make both sides the same first. trim() and toLowerCase() chain well for this, because each one returns a string:

const answer = "  Yes ";
console.log(answer === "yes");
console.log(answer.trim().toLowerCase() === "yes");

Output:

false
true

In the exercise, read a word, print it in capitals, check two things about it, and replace every "a" with "o".