---
title: "Avoid Soft 404 Errors in Client-Side Rendered SPAs"
description: "## **Problem** In SPAs, server can't always send meaningful HTTP status codes (like 404), which causes Google to think an error page is a valid page—leading to **soft 404 errors** and ranking issues. ## **Solutions** **JavaScript Redirect to a Server…"
url: "https://fsidm.in/knowledge/seo/avoid-soft-404-errors/"
updated: "2025-08-29"
category: SEO
---
# Avoid Soft 404 Errors in Client-Side Rendered SPAs
## **Problem**
In SPAs, server can't always send meaningful HTTP status codes (like 404), which causes Google to think an error page is a valid page—leading to **soft 404 errors** and ranking issues.
## **Solutions**
**JavaScript Redirect to a Server 404 Page** If content doesn’t exist, redirect the user to a real 404 page on your server that returns a proper 404 status code.
fetch(\`/api/products/${productId}\`)
.then(response => response.json())
.then(product => {
if (product.exists) {
showProductDetails(product);
} else {
window.location.href = '/not-found'; // 404 page from server
}
});
**Inject********on Error Pages** If redirect isn’t feasible, add a noindex meta tag dynamically to prevent Google from indexing the error page.
fetch(\`/api/products/${productId}\`)
.then(response => response.json())
.then(product => {
if (product.exists) {
showProductDetails(product);
} else {
const metaRobots = document.createElement('meta');
metaRobots.name = 'robots';
metaRobots.content = 'noindex';
document.head.appendChild(metaRobots);
}
});
## **Use the History API Instead of URL Fragments (****#****)**
**Bad practice (fragments):**
Products
- Google can’t reliably crawl URLs with fragments.
**Better practice (History API):**
Products
- Use JavaScript to update content **and** update the URL with history.pushState(), so Google can crawl and index properly.
## **Properly Inject****rel="canonical"****with JavaScript (If Needed)**
Dynamically add one correct canonical tag only:
fetch('/api/cats/' + id)
.then(res => res.json())
.then(cat => {
const linkTag = document.createElement('link');
linkTag.setAttribute('rel', 'canonical');
linkTag.href = \`https://example.com/cats/${cat.urlFriendlyName}\`;
document.head.appendChild(linkTag);
});
Avoid multiple or conflicting canonical tags.
## **Use Robots Meta Tags Carefully**
- Avoid placing in your original HTML if you want pages indexed.
- Adding noindex via JavaScript **won't work if Google skips rendering due to an initial noindex**.
- Use JavaScript to add or change the robots tag **only if** the page is indexable by default.
## **Additional Best Practices for JavaScript SEO in SPAs**
- **Long-lived caching with fingerprinting:** Use file names like main.2bb85551.js so browsers and Google fetch fresh resources when content changes.
- **Structured data with JSON-LD:** Inject structured data dynamically but test with Rich Results Test to avoid errors.
- **Web components:** Use slots to expose shadow DOM content to Google’s rendering engine so it indexes correctly.
- **Lazy-loading images:** Use search-friendly lazy loading following Google’s guidelines.
- **Accessibility:** Test your site with JavaScript disabled to ensure basic content is still accessible for all users and bots.
## **Avoid Soft 404 Errors in Client-Side Rendered SPAs**
### **Problem**
In SPAs, server can't always send meaningful HTTP status codes (like 404), which causes Google to think an error page is a valid page—leading to **soft 404 errors** and ranking issues.
### **Solutions**
**JavaScript Redirect to a Server 404 Page** If content doesn’t exist, redirect the user to a real 404 page on your server that returns a proper 404 status code.
fetch(\`/api/products/${productId}\`)
.then(response => response.json())
.then(product => {
if (product.exists) {
showProductDetails(product);
} else {
window.location.href = '/not-found'; // 404 page from server
}
});
**Inject********on Error Pages** If redirect isn’t feasible, add a noindex meta tag dynamically to prevent Google from indexing the error page.
fetch(\`/api/products/${productId}\`)
.then(response => response.json())
.then(product => {
if (product.exists) {
showProductDetails(product);
} else {
const metaRobots = document.createElement('meta');
metaRobots.name = 'robots';
metaRobots.content = 'noindex';
document.head.appendChild(metaRobots);
}
});
## **Use the History API Instead of URL Fragments (****#****)**
**Bad practice (fragments):**
Products
- Google can’t reliably crawl URLs with fragments.
**Better practice (History API):**
Products
- Use JavaScript to update content **and** update the URL with history.pushState(), so Google can crawl and index properly.
## **Properly Inject****rel="canonical"****with JavaScript (If Needed)**
Dynamically add one correct canonical tag only:
fetch('/api/cats/' + id)
.then(res => res.json())
.then(cat => {
const linkTag = document.createElement('link');
linkTag.setAttribute('rel', 'canonical');
linkTag.href = \`https://example.com/cats/${cat.urlFriendlyName}\`;
document.head.appendChild(linkTag);
});
Avoid multiple or conflicting canonical tags.
## **Use Robots Meta Tags Carefully**
- Avoid placing in your original HTML if you want pages indexed.
- Adding noindex via JavaScript **won't work if Google skips rendering due to an initial noindex**.
- Use JavaScript to add or change the robots tag **only if** the page is indexable by default.
## **Additional Best Practices for JavaScript SEO in SPAs**
- **Long-lived caching with fingerprinting:** Use file names like main.2bb85551.js so browsers and Google fetch fresh resources when content changes.
- **Structured data with JSON-LD:** Inject structured data dynamically but test with Rich Results Test to avoid errors.
- **Web components:** Use slots to expose shadow DOM content to Google’s rendering engine so it indexes correctly.
- **Lazy-loading images:** Use search-friendly lazy loading following Google’s guidelines.
- **Accessibility:** Test your site with JavaScript disabled to ensure basic content is still accessible for all users and bots.