JS: String.prototype.substring

str.substring(start, end)

Same as str.slice(start, end) but if any argument is negative, it is replaced with 0, and if any argument is greater than length, it's replaced by length.

• JS: String.prototype.slice

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

console.log("abcd".substring(0, "abcd".length) === "abcd");
console.log("abcd".substring() === "abcd");
console.log("abcd".substring(1) === "bcd");

console.log("abcd".substring(-1) === "abcd");
console.log("abcd".substring(-2) === "abcd");