How do I set specific ranges of an ArrayBuffer to random numbers?

I would like to set the first 29 bits of a 16-byte ArrayBuffer to a random value in the range [0, 2^28 - 1], independently of the system endianness.

Following is my attempt, but this (potentially) sets all 32 bits. What can I do? Is there a way to do something like randomNumberHere | 0x1FFFFFFF?

let buffer = new ArrayBuffer(16);
let view = new Uint32Array(buffer.slice(0, 4));
window.crypto.getRandomValues(view);