{"record":{"id":"17f68b78ab708937","repo":"vuejs/vue","slug":"function-template-is-only-supported-in-rendertostr","errorCode":null,"errorMessage":"function template is only supported in renderToString.","messagePattern":"function template is only supported in renderToString\\.","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"packages/server-renderer/src/create-renderer.ts","lineNumber":143,"sourceCode":" if (context) {\n templateRenderer.bindRenderFns(context)\n }\n const renderStream = new RenderStream((write, done) => {\n // @ts-expect-error\n render(component, write, context, done)\n })\n if (!template) {\n // @ts-expect-error\n if (context && context.rendered) {\n // @ts-expect-error\n const rendered = context.rendered\n renderStream.once('beforeEnd', () => {\n rendered(context)\n })\n }\n return renderStream\n } else if (typeof template === 'function') {\n throw new Error(\n `function template is only supported in renderToString.`\n )\n } else {\n const templateStream = templateRenderer.createStream(context)\n renderStream.on('error', err => {\n templateStream.emit('error', err)\n })\n renderStream.pipe(templateStream)\n //@ts-expect-error\n if (context && context.rendered) {\n //@ts-expect-error\n const rendered = context.rendered\n renderStream.once('beforeEnd', () => {\n rendered(context)\n })\n }\n return templateStream\n }","sourceCodeStart":125,"sourceCodeEnd":161,"githubUrl":"https://github.com/vuejs/vue/blob/9e88707940088cb1f4cd7dd210c9168a50dc347c/packages/server-renderer/src/create-renderer.ts#L125-L161","documentation":"Thrown synchronously from renderer.renderToStream when the template option is a function. Function templates require the full rendered content up front (they receive content + context and return a string or promise), but renderToStream pipes output incrementally through a TemplateStream — there is no single moment where the complete content is available to hand to a function. Only renderToString supports function templates because it accumulates the full string first.","triggerScenarios":"Calling renderer.renderToStream(app, context) on a renderer created with { template: (content, ctx) => html } where template is a function rather than a string.","commonSituations":"Developer reuses a renderer configured for renderToString (with a function template) and calls renderToStream on the same instance. Migrating from string template to programmatic template without realizing stream rendering doesn't support it.","solutions":["Use renderToString instead of renderToStream when a function template is required.","If streaming is mandatory, switch the template to a string (HTML with placeholder) so createStream can build a TemplateStream.","Create two renderers: one with a string template for streaming, one without a template and do post-processing on the stream manually."],"exampleFix":"// before\nconst renderer = createRenderer({\n template: (content, ctx) => `...${content}...`\n})\nrenderer.renderToStream(app) // throws\n\n// after — use renderToString for function templates\nrenderer.renderToString(app, (err, html) => { /* ... */ })","handlingStrategy":"validation","validationCode":"function assertTemplateCompatibleWithStream(template: unknown): void {\n if (typeof template === 'function') {\n throw new Error(\n 'Function templates are not supported by renderToStream. Use renderToString, or pass a string template.'\n )\n }\n}\n\nassertTemplateCompatibleWithStream(rendererOptions.template)\nrenderer.renderToStream(app)","typeGuard":"function isStreamCompatibleTemplate(template: unknown): boolean {\n return template === undefined || typeof template === 'string'\n}","tryCatchPattern":"try {\n renderer.renderToStream(app, context)\n} catch (e) {\n if (e.message.includes('function template is only supported in renderToString')) {\n // fall back to renderToString\n renderer.renderToString(app, context, cb)\n } else {\n throw e\n }\n}","preventionTips":["Use two renderer instances: one for stream (string template), one for toString (function template).","Document which render method each renderer is configured for.","Add a startup assertion: if template is a function, warn that renderToStream is unavailable."],"tags":["ssr","render-to-stream","template","streaming","api-mismatch"],"analyzedSha":"9e88707940088cb1f4cd7dd210c9168a50dc347c","analyzedAt":"2026-08-11T22:22:01.295Z","schemaVersion":2},"datasetVersion":"2026-08-12T05:08:24.936Z"}