A generic, dynamically sized TypedArray in TypeScript

dynamicArray.ts

interface TypedArray {
    readonly length : number;
    readonly [n: number]: number;
    BYTES_PER_ELEMENT : number;
    set(n : ArrayLike<number>, offset : number) : void;
}

interface TypedArrayConstructor<T extends TypedArray> {
    new (buffer: ArrayBuffer, byteOffset?: number, length?: number): T;
}

export class DynamicArray<T extends TypedArray, C extends TypedArrayConstructor<T>> {
    private buf : ArrayBuffer;
    arr : T;
    arrConstructor : C;

    constructor(arrayConstructor : C){
        this.arrConstructor = arrayConstructor;
        this.buf = new ArrayBuffer(8);
        this.arr = new this.arrConstructor(this.buf, 0, 0);        
    }

    push(a : T) {
        let nreq = (this.arr.length + a.length) * this.arr.BYTES_PER_ELEMENT;
        let requiresExpand = nreq >= this.buf.byteLength;
        if (requiresExpand) {
            // find the new required array length
            let nlen = this.buf.byteLength * 2;
            while (nlen < nreq){
                nlen *= 2;
            }

            // allocate new buffer
            let nbuf = new ArrayBuffer(nlen);
            
            // copy the original array into the new buffer
            let narr = new this.arrConstructor(nbuf, 0, this.arr.length);
            narr.set(this.arr, 0);

            // set the new buf
            this.buf = nbuf;
            this.arr = narr;
        }

        let l0 = this.arr.length;
        this.arr = new this.arrConstructor(this.buf, 0, l0 + a.length);
        this.arr.set(a, l0)
    }
}