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Encrypting data with AES128 in JavaScript

Usage

AES128 uses a 16 byte secret key.

const key = new Uint8Array(16);
crypto.getRandomValues(key);

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function generateRandomInteger(max: number): number {
    if (max < 0 || !Number.isInteger(max)) {
        throw new Error("Argument 'max' must be an integer greater than or equal to 0")
    }
    const bitLength = (max - 1).toString(2).length
    const shift = bitLength % 8
    const bytes = new Uint8Array(Math.ceil(bitLength / 8))
    while (true) {
        crypto.getRandomValues(bytes)
        // This zeroes bits that can be ignored to increase the chance `result` < `max`.

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function random(): number {
	const buffer = new ArrayBuffer(8);
	const bytes = crypto.getRandomValues(new Uint8Array(buffer));
  
	// sets the exponent value (11 bits) to 01111111111 (1023)
	// since the bias is 1023 (2 * (11 - 1) - 1), 1023 - 1023 = 0
	// 2^0 * (1 + [52 bit number between 0-1]) = number between 1-2
	bytes[0] = 63;
	bytes[1] = bytes[1] | 240;