TypeScript implementation of fast cumulative sum

cumulativeSum.ts

class CumulativeSum {
    private sums: number[] = [0];

    constructor(itr: Iterable<number>) {
        const values = [...itr];

        for (let i = 0; i < values.length; ++i) {
            this.sums[i + 1] = this.sums[i] + values[i];
        }
    }

    get(from: number, to: number) {
        if (to < 0) return 0;
        from = Math.max(from, 0);
        to = Math.min(to, this.sums.length - 2);

        return this.sums[to + 1] - this.sums[from];
    }
}