search.js

import { useMemo } from "react"
import { useStaticQuery } from "gatsby"

export const useSearch = (searching) => {
  const { allMarkdownRemark } = useStaticQuery(graphql`
    query {
      allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] },
      ) {
        edges {
          node {
            fields { slug }
            frontmatter {
              title
              date
            }
            rawMarkdownBody
          }
        }
      }
    }
  `)

  const index = useMemo(() => allMarkdownRemark.edges.map(({ node }) => ({
    slug: node.fields.slug,
    title: node.frontmatter.title,
    date: node.frontmatter.date,
    body: node.rawMarkdownBody,
  })), [allMarkdownRemark.edges])

  const results = useMemo(() => {
    const words = searching.toLowerCase().split(/\s+/)
    return index.filter(item =>
      [item.slug, item.title, item.body].some(content => words.some(word => content.toLowerCase().includes(word)))
    )
  }, [index, searching])

  return results
}