How to Fix React Hydration Error in Next.js

React hydration errors in Next.js can be frustrating especially when you are building a blog page using the WordPress REST API and rendering HTML content like excerpt.rendered.

If you’re seeing errors like:

• Hydration failed because the initial UI does not match what was rendered on the server
• Text content does not match server-rendered HTML
• Expected server HTML to contain a matching

don’t worry. This guide explains why it happens and provides a complete working fix for WordPress + Next.js.

What is a Hydration Error in Next.js?

Next.js renders your page in two steps:

1. Server-Side Rendering (SSR): HTML is generated on the server.
2. Client Hydration: React runs in the browser and attaches event handlers to the existing HTML.

A hydration error happens when:

The server renders one HTML structure
But the browser React render produces something slightly different

Even one small difference like an extra <p>, whitespace, or a different tag structure can trigger hydration problems.

Why This Happens with WordPress REST API Content

WordPress often returns HTML inside fields such as:

• title.rendered
• excerpt.rendered
• content.rendered

Example excerpt coming from WP API:

<p>If you have heard that there are ways to make money while shopping in the UAE and would like...</p>

When you render that using certain parsing methods (like react-html-parser), the server output may differ from the client output.

Common Causes of Hydration Error in Your Setup

Using react-html-parser in SSR:

Libraries like react-html-parser can produce different results in Node.js (server) vs browser (client), causing mismatched markup.

Invalid HTML nesting:

Your code wraps HTML output inside <p className="expert"> ... </p> but WordPress excerpt already contains <p> tags.

That creates invalid HTML like:

<p class="expert">
  <p>WordPress paragraph here</p>
</p>

Browsers “fix” invalid HTML differently than React expects → hydration mismatch.

Using unstable keys (key={i}):

Using index keys can cause React to mismatch elements if data order changes or updates between renders.

Your Original Code (Problem Area)

This line causes the biggest issue:

<p className="expert">{ReactHtmlParser(x.excerpt.rendered)}</p>

Because x.excerpt.rendered already contains <p>...</p> tags.

The Best Fix (Recommended for Next.js + WordPress)

Replace react-html-parser with dangerouslySetInnerHTML

This renders the same HTML string on both server and client, preventing hydration mismatches.

Also: Don’t wrap WP HTML inside <p>

Use a <div> instead.

Final Fixed Code (Complete Working Solution)

import React, { Component } from "react";
import Link from "next/link";
import { BiCalendar } from "react-icons/bi";export default class Blog extends Component {
  constructor(props) {
    super(props);
    this.state = {
      data: props.bloglist || [],
    };
  }  render() {
    const { data } = this.state;
    if (!data || data.length === 0) return null;    return (
      <div className="container blog-section">
        <div className="row">
          <h2>Latest Posts</h2>
        </div>        <div className="row">
          {data.map((x) => (
            <div className="col-md-4 boxs text-center" key={x.id}>
              <div className="bg-info">
                <img
                  src={x?.images?.large}
                  className="img-fluid"
                  alt={x?.title?.rendered || "Post image"}
                />                <h3>{x?.title?.rendered}</h3>                <p className="shopping">
                  <span>
                    <BiCalendar /> {x?.date}
                  </span>
                </p>                {/* FIX: Render WordPress HTML safely without parsing mismatch */}
                <div
                  className="expert"
                  dangerouslySetInnerHTML={{ __html: x?.excerpt?.rendered || "" }}
                />                <Link href={`/blog/${x.slug}/${x.id}`}>
                  <div className="readmore">
                    <span>Readmore</span>
                  </div>
                </Link>
              </div>
            </div>
          ))}
        </div>
      </div>
    );
  }
}

Why This Fix Works

dangerouslySetInnerHTML renders the same HTML string on the server and client
avoids SSR vs browser parsing differences
no invalid nested <p> tags
stable React keys (key={x.id})

Bonus: Make It More Secure (Highly Recommended)

Because WordPress content can contain unwanted HTML, you should sanitize it.

A common option is sanitize-html.

Install:

npm install sanitize-html

Use:

import sanitizeHtml from "sanitize-html";const cleanHTML = sanitizeHtml(x?.excerpt?.rendered || "", {
  allowedTags: sanitizeHtml.defaults.allowedTags,
  allowedAttributes: {
    a: ["href", "target", "rel"],
    img: ["src", "alt"],
  },
});

Then:

<div dangerouslySetInnerHTML={{ __html: cleanHTML }} />

Conclusion

If you’re using WordPress REST API in Next.js and rendering excerpt.rendered, hydration errors usually come from invalid HTML nesting and differences between server and client parsing.