SyntaxShelf
JS

Strings

JavaScript · 10 entries

Template Literals

syntax
`text ${expression} text`
example
const item = "coffee";
const price = 4.5;
console.log(`One ${item} costs $${price.toFixed(2)}.`);

const multiline = `Line one
Line two
Line three`;
console.log(multiline);
output
"One coffee costs $4.50."
"Line one\nLine two\nLine three"

Note Backtick strings support embedded expressions and multiline content without escape characters.

template literalstring interpolationbacktick stringmultiline stringembed expression in string

Tagged Templates

syntax
tagFunction`text ${expr} text`
example
function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    return result + str + (values[i] !== undefined ? `[${values[i]}]` : "");
  }, "");
}
const user = "Kai";
console.log(highlight`Welcome, ${user}! You have ${3} alerts.`);
output
"Welcome, [Kai]! You have [3] alerts."

Note Tagged templates let you process template literal parts before producing the final string. Used in libraries like styled-components and GraphQL.

tagged templatetemplate tag functionprocess template literal

String Searching

syntax
str.includes(search, startIndex)
str.startsWith(search)
str.endsWith(search)
example
const msg = "Order #1234 shipped";
console.log(msg.includes("shipped"));   // true
console.log(msg.startsWith("Order"));   // true
console.log(msg.endsWith("shipped"));   // true
console.log(msg.indexOf("#"));          // 6

Note All search methods are case-sensitive. For case-insensitive checks, lowercase both sides first: str.toLowerCase().includes(term.toLowerCase()).

string containscheck if string includesstarts withends withfind in string

Extracting Substrings

syntax
str.slice(start, end)
str.substring(start, end)
example
const path = "/users/profile/avatar.png";
console.log(path.slice(1));          // "users/profile/avatar.png"
console.log(path.slice(-10));        // "avatar.png"
console.log(path.slice(7, 14));      // "profile"

Note slice() supports negative indices (counts from end). substring() does not. Prefer slice() -- it is more predictable.

substringslice stringextract part of stringget characters from string

Replacing Text

syntax
str.replace(search, replacement)
str.replaceAll(search, replacement)
example
const template = "Hello {name}, welcome to {place}!";
const filled = template
  .replace("{name}", "Ava")
  .replace("{place}", "Berlin");
console.log(filled);

const csv = "a,b,c,d";
console.log(csv.replaceAll(",", " | "));
output
"Hello Ava, welcome to Berlin!"
"a | b | c | d"

Note replace() only swaps the first match unless you use a regex with the /g flag. replaceAll() replaces every occurrence.

replace stringstring replacereplace all occurrencesfind and replace

Split and Join

syntax
str.split(separator, limit)
arr.join(separator)
example
const tags = "js,react,node";
const tagArray = tags.split(",");
console.log(tagArray);
console.log(tagArray.join(" + "));
output
["js", "react", "node"]
"js + react + node"

Note split("") splits into individual characters. split() with no arguments returns the entire string in a single-element array.

split stringjoin array to stringstring to arrayseparate by delimiter

Trimming Whitespace

syntax
str.trim()
str.trimStart()
str.trimEnd()
example
const input = "  hello@example.com  ";
console.log(input.trim());       // "hello@example.com"
console.log(input.trimStart());  // "hello@example.com  "
console.log(input.trimEnd());    // "  hello@example.com"

Note Essential for cleaning user input. Only removes whitespace characters (spaces, tabs, newlines), not other invisible characters.

trim whitespaceremove spacestrim stringclean input

Padding Strings

syntax
str.padStart(targetLength, padChar)
str.padEnd(targetLength, padChar)
example
const orderNum = "42";
console.log(orderNum.padStart(6, "0"));  // "000042"

const label = "Price";
console.log(label.padEnd(12, "."));      // "Price......."

Note Useful for formatting IDs, aligning columns in console output, or zero-padding numbers.

pad stringpadStartpadEndzero padformat string length

Case Conversion

syntax
str.toUpperCase()
str.toLowerCase()
str.toLocaleUpperCase(locale)
example
const status = "Pending";
console.log(status.toUpperCase());  // "PENDING"
console.log(status.toLowerCase());  // "pending"

// Locale-aware (e.g., Turkish "i" -> "I" with dot)
console.log("istanbul".toLocaleUpperCase("tr"));

Note Always use locale-aware methods when dealing with internationalized text. The Turkish i is a classic bug source.

uppercaselowercaseconvert casecapitalize string

Repeat and Character Access

syntax
str.repeat(count)
str.at(index)
example
const border = "=".repeat(30);
console.log(border);

const word = "JavaScript";
console.log(word.at(0));   // "J"
console.log(word.at(-1));  // "t"

Note at() supports negative indices to count from the end. Bracket notation str[-1] returns undefined, not the last character.

repeat stringget last characterstring atcharacter at index