JS: String.prototype.slice

str.slice(start)

Return a substring from index start to end.

console.log("abcd".slice(1, 3) === "bc");

str.slice(start, end)

Return a substring from index start to end.

console.log("abcd".slice(0, "abcd".length) === "abcd");
console.log("abcd".slice() === "abcd");
console.log("abcd".slice(1) === "bcd");
console.log("abcd".slice(-1) === "d");
console.log("abcd".slice(-2) === "cd");

// same index, empty string
console.log("abcd".slice(2, 2) === "");

// when start index is greater than end index, result is empty string
console.log("abcd".slice(3, 2) === "");
console.log("abcd".slice(-2, -3) === "");

🛑 warning: if string contains emoji (🦋) or rarely used unicode character, result of string methods may not be what you expect. See JS: String Index and Code Unit

// correct way to take a substring of string that contains emoji.
console.assert(Array.from("🦋bc").slice(0, 2).join("") === "🦋b");

// if you just use slice , you get incorrect result.
console.assert("a🦋bc".slice(0, 2) === "a🦋" === false);