JavaScript Cheatsheet

String methods

// Obtaining portions of a string
s.substring(1, 4); // => "ell": the 2nd, 3rd, and 4th characters.
s.slice(1, 4); // => "ell": same thing
s.slice(-3); // => "rld": last 3 characters
s.split(", "); // => ["Hello", "world"]: split at delimiter string

// Searching a string
s.indexOf("l"); // => 2: position of first letter l
s.indexOf("l", 3); // => 3: position of first "l" at or after 3
s.indexOf("zz"); // => -1: s does not include the substring "zz"
s.lastIndexOf("l"); // => 10: position of last letter l

// Boolean searching functions in ES6 and later
s.startsWith("Hell"); // => true: the string starts with these
s.endsWith("!"); // => false: s does not end with that
s.includes("or"); // => true: s includes substring "or"

// Creating modified versions of a string
s.replace("llo", "ya"); // => "Heya, world"
s.toLowerCase(); // => "hello, world"
s.toUpperCase(); // => "HELLO, WORLD"
s.normalize(); // Unicode NFC normalization: ES6
s.normalize("NFD"); // NFD normalization. Also "NFKC", "NFKD"

// Inspecting individual (16-bit) characters of a string
s.charAt(0); // => "H": the first character

// String padding functions in ES2017
"x".padStart(3); // => "  x": add spaces on the left to a length of 3
"x".padEnd(3); // => "x  ": add spaces on the right to a length of 3
"x".padStart(3, "*"); // => "**x": add stars on the left to a length of 3
"x".padEnd(3, "-"); // => "x--": add dashes on the right to a length of 3

// Space trimming functions. trim() is ES5; others ES2019
" test ".trim(); // => "test": remove spaces at start and end
" test ".trimStart(); // => "test ": remove spaces on left. Also trimLeft
" test ".trimEnd(); // => " test": remove spaces at right. Also trimRight