TopolearnMost programs spend a lot of time building, slicing and checking text.
Strings can use single quotes, double quotes or backticks. Backticks create template literals, which allow interpolation with ${expression} and can span multiple lines:
const msg = `Hello ${user.name}, you have ${count + 1} items`;Strings are immutable: every method returns a new string and leaves the original alone. The ones you'll use constantly:
length,str[0],str.at(-1)(negative indexes count from the end)includes,startsWith,endsWith,indexOfslice(start, end)— end is exclusive; negatives count from the endtoUpperCase,toLowerCase,trim,trimStart,trimEndsplit(separator)to get an array, andarray.join(sep)to go backreplace(first match) andreplaceAll(every match)padStart(len, ch)for things like zero-padding:"7".padStart(3, "0")is"007"repeat(n)
Comparison with < and > compares UTF-16 code units, so "Z" < "a" is true. For human-facing sorting use a.localeCompare(b) or Intl.Collator.
One Unicode gotcha: length counts UTF-16 code units, so an emoji outside the basic plane (like "😀") has length 2. Iterating with for...of or spreading [...str] walks whole code points instead, which is what you usually want for user text.
Escape sequences such as \n (newline) and \t (tab) work in all three quote styles.
Example
const name = "Ada Lovelace";
console.log(`Hi ${name.split(" ")[0]}!`); // Hi Ada!
console.log(name.length); // 12
console.log(name.slice(0, 3)); // "Ada"
console.log(name.at(-1)); // "e"
console.log(name.includes("Love")); // true
console.log(name.toUpperCase()); // "ADA LOVELACE"
const csv = " a, b ,c ";
console.log(csv.split(",").map(s => s.trim())); // [ 'a', 'b', 'c' ]
console.log("2-5-2025".replaceAll("-", "/")); // "2/5/2025"
console.log(String(7).padStart(3, "0")); // "007"
console.log("😀".length, [..."😀"].length); // 2 1Remember
- Template literals: backticks plus
${expr}for interpolation and multi-line text - String methods never modify the original — they return a new string
lengthcounts UTF-16 units; use[...str]to count characters users see as one
Watch out for
- Calling
str.replace("a", "b")and expecting every match replaced — usereplaceAll.