Pagination generator

pagination.js

function paginate(
    curPosition = 1,
    maxPosition = 10,
    listSize = 7,
    minPosition = 1
) {
    curPosition = Math.max(minPosition, Math.min(maxPosition, curPosition));

    const half = Math.floor(listSize / 2);
    let start = curPosition - half;
    let end = curPosition + half;

    if (start < minPosition) {
        end += minPosition - start;
        start = minPosition;
    }
    if (end > maxPosition) {
        start -= end - maxPosition;
        end = maxPosition;
    }
    start = Math.max(start, minPosition);

    const result = [];

    for (let i = start; i <= end && result.length < listSize; i++) {
        result.push(i);
    }

    result[0] = minPosition;
    result[result.length - 1] = maxPosition;

    if ((result[1] - result[0]) > 1) {
        result[1] = 0; // '...'
    }

    const lastIdx = result.length - 1;
    if ((result[lastIdx] - result[lastIdx - 1]) > 1) {
        result[lastIdx - 1] = 0; // '...'
    }

    const pages = result.map(function(item) {
        return {
            label: item !== 0 ? String(item) : '...',
            value: item !== 0 ? item : null,
            isCurrent: item === curPosition
        };
    });

    pages.unshift({
        label: 'Prev',
        value: curPosition > minPosition ? curPosition - 1 : null,
        isCurrent: false
    });

    pages.push({
        label: 'Next',
        value: curPosition < maxPosition ? curPosition + 1 : null,
        isCurrent: false
    });

    return pages;
}

pagination.ts

type PageItem = {
    label: string;
    value: number | null;
    isCurrent: boolean;
};

export function paginate(
    curPosition: number = 1,
    maxPosition: number = 10,
    listSize: number = 7,
    minPosition: number = 1
): PageItem[] {
    // ...
    curPosition = Math.max(minPosition, Math.min(maxPosition, curPosition));

    const half = Math.floor(listSize / 2);
    let start = curPosition - half;
    let end = curPosition + half;

    if (start < minPosition) {
        end += minPosition - start;
        start = minPosition;
    }
    if (end > maxPosition) {
        start -= end - maxPosition;
        end = maxPosition;
    }
    start = Math.max(start, minPosition);

    const result: (number)[] = [];

    for (let i = start; i <= end && result.length < listSize; i++) {
        result.push(i);
    }

    // ...

    result[0] = minPosition;

    result[result.length - 1] = maxPosition;

    if ((result[1] - result[0]) > 1) {
        result[1] = 0; // '...';
    }

    const lastIdx = result.length - 1;
    if ((result[lastIdx] - result[lastIdx - 1]) > 1) {
        result[lastIdx - 1] = 0; // '...';
    }

    // ...

    const pages: PageItem[] = result.map((item): PageItem => ({
        label: item !== 0 ? `${item}` : '...',
        value: item !== 0 ? item : null,
        isCurrent: item === curPosition
    }));

    pages.unshift({
        label: 'Prev',
        value: curPosition > minPosition ? curPosition - 1 : null,
        isCurrent: false
    });

    pages.push({
        label: 'Next',
        value: curPosition < maxPosition ? curPosition + 1 : null,
        isCurrent: false
    });

    return pages;
}

import { paginate } from './pagination';

console.log('pagination', paginate(5, 10));

[
    {"label": "Prev", "value": 4, "isCurrent": false},
    {"label": "1", "value": 1, "isCurrent": false},
    {"label": "...", "value": null, "isCurrent": false},
    {"label": "4", "value": 4, "isCurrent": false},
    {"label": "5", "value": 5, "isCurrent": true},
    {"label": "6", "value": 6, "isCurrent": false},
    {"label": "...", "value": null, "isCurrent": false},
    {"label": "10", "value": 10, "isCurrent": false},
    {"label": "Next", "value": 6, "isCurrent": false},
]