Create pagination buttons array

Pagination.ts

class Pagination {
    private readonly page: number;
    private readonly pagesCount: number;
    private readonly delta: number;

    constructor(page: number, pagesCount: number) {
        this.page = page;
        this.pagesCount = pagesCount;
        this.delta = 2;
    }

    range = function* (start = 0, end = 0) {
        while (start <= end) {
            yield start++;
        }
    };

    getButtons = () => {
        const buttons = [];
        const before = this.page - this.delta > 1;
        const after = this.page + this.delta < this.pagesCount;
        const start = Math.max(
            before
                ? this.page -
                      this.delta -
                      (!after ? this.page - this.pagesCount + 1 + this.delta : 0)
                : 2,
            2
        );
        const end = Math.min(
            after
                ? this.page +
                      this.delta +
                      (!before ? 2 - this.page + this.delta : 0)
                : this.pagesCount - 1,
            this.pagesCount - 1
        );

        buttons.push(1);

        for (const i of this.range(start, end)) {
            buttons.push(i);
        }

        if (this.pagesCount !== 1) {
            buttons.push(this.pagesCount);
        }
        return buttons;
    };
}

const pagination = new Pagination(35, 40);
const buttons = pagination.getButtons();