render() — svelte Function Reference

Source Code

packages/svelte/src/internal/server/renderer.js lines 400–468

	static render(component, options = {}) {
		/** @type {AccumulatedContent | undefined} */
		let sync;
		/** @type {Promise<AccumulatedContent & { hashes: { script: Sha256Source[] } }> | undefined} */
		let async;

		const result = /** @type {RenderOutput} */ ({});
		// making these properties non-enumerable so that console.logging
		// doesn't trigger a sync render
		Object.defineProperties(result, {
			html: {
				get: () => {
					return (sync ??= Renderer.#render(component, options)).body;
				}
			},
			head: {
				get: () => {
					return (sync ??= Renderer.#render(component, options)).head;
				}
			},
			body: {
				get: () => {
					return (sync ??= Renderer.#render(component, options)).body;
				}
			},
			hashes: {
				value: {
					script: ''
				}
			},
			then: {
				value:
					/**
					 * this is not type-safe, but honestly it's the best I can do right now, and it's a straightforward function.
					 *
					 * @template TResult1
					 * @template [TResult2=never]
					 * @param { (value: SyncRenderOutput) => TResult1 } onfulfilled
					 * @param { (reason: unknown) => TResult2 } onrejected
					 */
					(onfulfilled, onrejected) => {
						if (!async_mode_flag) {
							const result = (sync ??= Renderer.#render(component, options));
							const user_result = onfulfilled({
								head: result.head,
								body: result.body,
								html: result.body,
								hashes: { script: [] }
							});
							return Promise.resolve(user_result);
						}
						async ??= init_render_context().then(() =>
							with_render_context(() => Renderer.#render_async(component, options))
						);
						return async.then((result) => {
							Object.defineProperty(result, 'html', {
								// eslint-disable-next-line getter-return
								get: () => {
									e.html_deprecated();
								}
							});
							return onfulfilled(/** @type {SyncRenderOutput} */ (result));
						}, onrejected);
					}
			}
		});

		return result;
	}