index.js

const path = require('path');

function getIntervallers(max, interval) {
	const count = Math.ceil(max / interval);
	const arr = [...Array(count)];
	return arr.map((v, index) => {
		const start = index * interval;
		const end = (index + 1) * interval - 1;
		return [start, end > max ? max : end];
	});
}

module.exports = (options, ctx) => ({
	enhanceAppFiles: [path.resolve(__dirname, 'clientPlugin.js')],

	ready() {
		let { postsFilter, postsSorter } = options;
		postsFilter = postsFilter || (({ type }) => type === 'post');
		postsSorter =
			postsSorter ||
			((prev, next) => {
				const prevTime = new Date(prev.frontmatter.date).getTime();
				const nextTime = new Date(next.frontmatter.date).getTime();
				return prevTime - nextTime > 0 ? -1 : 1;
			});

		const { pages } = ctx;
		const posts = pages.filter(postsFilter);
		const {
			perPagePosts = 5,
			paginationDir = 'page',
			firstPagePath = '/',
			layout = 'Layout'
		} = options;

		const intervallers = getIntervallers(posts.length, perPagePosts);
		const pagination = {
			paginationPages:
				intervallers.length !== 0
					? intervallers.map((interval, index) => {
							const path =
								index === 0 ? firstPagePath : `/${paginationDir}/${index + 1}/`;
							return { path, interval };
					  })
					: [],
			postsFilter: postsFilter.toString(),
			postsSorter: postsSorter.toString()
		};

		ctx.pagination = pagination;
		pagination.paginationPages.forEach(({ path }, index) => {
			if (path === '/') {
				return;
			}
			ctx.addPage({
				permalink: path,
				frontmatter: {
					layout,
					title: `Page ${index + 1}`
				}
			});
		});
	},

	async clientDynamicModules() {
		return {
			name: 'pagination.js',
			content: `export default ${JSON.stringify(ctx.pagination, null, 2)}`
		};
	}
});