Depending on what to use, but I think it's worth checking out this code snippet:
const str = "Hello World!"; // set string
const encoder = new TextEncoder(); // create an instance of the TextEncoder class
const strBytes = encoder.encode(str); // convert string to byte array
const sliceStart = 1; // set the beginning of the slice
const sliceEnd = 5; // set the end of the slice
const sliceBytes = strBytes.subarray(sliceStart, sliceEnd); // create a slice from an array of bytes
const decoder = new TextDecoder(); // create an instance of the TextDecoder class
const sliceStr = decoder.decode(sliceBytes); // convert slice back to string
console log(sliceStr); // output the result to the console