ssr:beforeRender Hook

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Hook Signature
Usage Example
Use Cases

The ssr:beforeRender hook is called before the server-side rendering process begins. This hook allows you to control whether the SSR rendering should proceed and is a good place to perform any initialization or checks specific to the server environment.

Hook Signature

export interface Hook {
  'ssr:beforeRender': (ctx: ShouldRenderContext) => HookResult
}

Parameters

Name	Type	Description
`ctx`	`ShouldRenderContext`	Context object with rendering control

The ShouldRenderContext interface is defined as:

interface ShouldRenderContext {
  shouldRender: boolean
}

Returns

HookResult which is either void or Promise<void>

Usage Example

import { createHead } from '@unhead/svelte'

const head = createHead({
  hooks: {
    'ssr:beforeRender': (ctx) => {
      // Log SSR rendering intent
      console.log('Preparing for server-side rendering of head tags')

      // You can prevent rendering by setting shouldRender to false
      if (process.env.SKIP_HEAD_RENDERING === 'true') {
        console.log('Skipping head tag rendering based on environment setting')
        ctx.shouldRender = false
      }
    }
  }
})

Use Cases

Conditional SSR Rendering

Control whether SSR rendering should proceed based on server conditions:

import { defineHeadPlugin } from '@unhead/svelte'

export const conditionalSsrPlugin = defineHeadPlugin({
  hooks: {
    'ssr:beforeRender': (ctx) => {
      // Only render head tags for specific routes or conditions
      const currentRoute = getCurrentRoute() // Your route detection logic

      // Skip head rendering for specific routes (e.g., API endpoints)
      if (currentRoute.startsWith('/api/')) {
        ctx.shouldRender = false
      }

      // Skip head rendering for certain user agents
      const userAgent = getUserAgent() // Your user-agent detection logic
      if (userAgent.includes('Googlebot') || userAgent.includes('crawler')) {
        // For bots, we might use a different rendering strategy
        ctx.shouldRender = false
      }
    }
  }
})

SSR Environment Setup

Set up the server environment before rendering:

import { defineHeadPlugin } from '@unhead/svelte'

export const ssrEnvironmentPlugin = defineHeadPlugin({
  hooks: {
    'ssr:beforeRender': () => {
      // Set up globalThis variables or state needed for SSR
      globalThis.__UNHEAD_SSR_ENABLED = true

      // Configure environment-specific settings
      if (process.env.NODE_ENV === 'development') {
        // In development, we might want to add debug information
        globalThis.__UNHEAD_DEBUG = true
      }

      // Prepare rendering context
      globalThis.__UNHEAD_RENDER_CONTEXT = {
        startTime: process.hrtime(),
        renderer: 'node',
        version: process.version
      }
    }
  }
})

Performance Optimization

Skip unnecessary rendering for performance optimization:

import { defineHeadPlugin } from '@unhead/svelte'

export const ssrPerformancePlugin = defineHeadPlugin({
  hooks: {
    'ssr:beforeRender': (ctx) => {
      // Cache key based on current request
      const cacheKey = generateCacheKey() // Your cache key generation logic

      // Check if we have a cached version of the head HTML
      if (globalThis.__UNHEAD_CACHE && globalThis.__UNHEAD_CACHE[cacheKey]) {
        // Skip rendering and use cached value later
        ctx.shouldRender = false

        // Store cache key for later retrieval
        globalThis.__UNHEAD_CURRENT_CACHE_KEY = cacheKey

        console.log('Using cached head HTML, skipping rendering')
      }
      else {
        // Prepare to render and cache
        globalThis.__UNHEAD_CURRENT_CACHE_KEY = cacheKey
      }
    }
  }
})