JavaScript Tutorial · JavaScript Basics · Lesson 9 of 44
JavaScript String Methods
Search, slice, replace, split, trim and pad strings.
Changing case and trimming
const s = " Hello World ";
console.log(s.trim());
console.log(s.toUpperCase());
console.log(s.trim().toLowerCase());
console.log("7".padStart(3, "0"));
console.log("ha".repeat(3));
Output
Hello World HELLO WORLD hello world 007 hahaha
Searching
includes(), startsWith() and endsWith() return booleans; indexOf() returns the position or -1:
const email = "[email protected]";
console.log(email.includes("@"));
console.log(email.endsWith(".com"));
console.log(email.startsWith("admin"));
console.log(email.indexOf("@"));
console.log(email.indexOf("#"));
Output
true true false 3 -1
Extracting and replacing
slice(start, end) extracts part of a string (negative numbers count from the end). replaceAll() replaces every match; replace() only the first:
const text = "I like cats. cats are great.";
console.log(text.slice(2, 6));
console.log(text.slice(-6));
console.log(text.replace("cats", "dogs"));
console.log(text.replaceAll("cats", "dogs"));
Output
like great. I like dogs. cats are great. I like dogs. dogs are great.
Splitting and joining
split() turns a string into an array; an array's join() turns it back:
const csv = "red,green,blue";
const colors = csv.split(",");
console.log(colors);
console.log(colors.join(" | "));
console.log("hello".split("").reverse().join(""));
Output
[ 'red', 'green', 'blue' ] red | green | blue olleh
Test yourself
What does "JavaScript".slice(0, 4) return?
"Java""JavaS""avaS""Script"
Show answer
Answer: "Java"