Activation Keys JS Fundamentals

function activationKeys(arr) {
    let string = arr.shift();

    for (let line of arr) {
        let instructions = line.split(">>>");

        if (instructions[0] === "Contains") {
            if (string.includes(instructions[1])) {
                console.log(`${string} contains ${instructions[1]}`);
            } else {
                console.log("Substring not found!");
            }
        } else if (instructions[0] === "Flip") {
            let startIndex = Number(instructions[2]);
            let endIndex = Number(instructions[3]);
            let substring = string.substring(startIndex, endIndex);

            if (instructions[1] === "Upper") {
                substring = substring.toUpperCase();
            } else {
                substring = substring.toLowerCase();
            }

            string = string.slice(0, startIndex) + substring + string.slice(endIndex);
            console.log(string);
        } else if (instructions[0] === "Slice") {
            let startIndex = Number(instructions[1]);
            let endIndex = Number(instructions[2]);

            string = string.slice(0, startIndex) + string.slice(endIndex);
            console.log(string);
        } else if (instructions[0] === "Generate") {
            console.log(`Your activation key is: ${string}`);
        }
    }
}