feat(json)!: add json.stringify: 'auto' and make that the default

docs/config/shared-options.md

@@ -343,12 +343,12 @@ Whether to support named imports from `.json` files.
 
 ## json.stringify
 
-- **Type:** `boolean`
-- **Default:** `false`
+- **Type:** `boolean | 'auto'`
+- **Default:** `'auto'`
 
 If set to `true`, imported JSON will be transformed into `export default JSON.parse("...")` which is significantly more performant than Object literals, especially when the JSON file is large.
 
-Enabling this disables named imports.
+If set to `'auto'`, the data will be stringified only if the data is bigger than 10kB.
 
 ## esbuild
 

packages/vite/src/node/__tests__/plugins/json.spec.ts

@@ -1,5 +1,9 @@
-import { expect, test } from 'vitest'
-import { extractJsonErrorPosition } from '../../plugins/json'
+import { describe, expect, test } from 'vitest'
+import {
+  type JsonOptions,
+  extractJsonErrorPosition,
+  jsonPlugin,
+} from '../../plugins/json'
 
 const getErrorMessage = (input: string) => {
   try {
@@ -24,3 +28,109 @@ test('can extract json error position', () => {
     )
   }
 })
+
+describe('transform', () => {
+  const transform = (input: string, opts: JsonOptions, isBuild: boolean) => {
+    const plugin = jsonPlugin(opts, isBuild)
+    return (plugin.transform! as Function)(input, 'test.json').code
+  }
+
+  test('namedExports: true, stringify: false', () => {
+    const actual = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: true, stringify: false },
+      false,
+    )
+    expect(actual).toMatchInlineSnapshot(`
+      "export const a = 1;
+      export default {
+      	a: a,
+      	"🫠": "",
+      	"const": false
+      };
+      "
+    `)
+  })
+
+  test('namedExports: false, stringify: false', () => {
+    const actual = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: false, stringify: false },
+      false,
+    )
+    expect(actual).toMatchInlineSnapshot(`
+      "export default {
+      	a: 1,
+      	"🫠": "",
+      	"const": false
+      };"
+    `)
+  })
+
+  test('namedExports: true, stringify: true', () => {
+    const actual = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: true, stringify: true },
+      false,
+    )
+    expect(actual).toMatchInlineSnapshot(`
+      "export const a = 1;
+      export default {
+        a,
+        "🫠": "",
+        "const": false,
+      };
+      "
+    `)
+  })
+
+  test('namedExports: false, stringify: true', () => {
+    const actualDev = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: false, stringify: true },
+      false,
+    )
+    expect(actualDev).toMatchInlineSnapshot(
+      `"export default JSON.parse("{\\"a\\":1,\\n\\"🫠\\": \\"\\",\\n\\"const\\": false}")"`,
+    )
+
+    const actualBuild = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: false, stringify: true },
+      true,
+    )
+    expect(actualBuild).toMatchInlineSnapshot(
+      `"export default JSON.parse("{\\"a\\":1,\\"🫠\\":\\"\\",\\"const\\":false}")"`,
+    )
+  })
+
+  test("namedExports: true, stringify: 'auto'", () => {
+    const actualSmall = transform(
+      '{"a":1,\n"🫠": "",\n"const": false}',
+      { namedExports: true, stringify: 'auto' },
+      false,
+    )
+    expect(actualSmall).toMatchInlineSnapshot(`
+      "export const a = 1;
+      export default {
+        a,
+        "🫠": "",
+        "const": false,
+      };
+      "
+    `)
+    const actualLargeNonObject = transform(
+      `{"a":1,\n"🫠": "${'vite'.repeat(3000)}",\n"const": false}`,
+      { namedExports: true, stringify: 'auto' },
+      false,
+    )
+    expect(actualLargeNonObject).not.toContain('JSON.parse(')
+
+    const actualLarge = transform(
+      `{"a":1,\n"🫠": {\n"foo": "${'vite'.repeat(3000)}"\n},\n"const": false}`,
+      { namedExports: true, stringify: 'auto' },
+      false,
+    )
+    expect(actualLarge).toContain('JSON.parse(')
+  })
+})

packages/vite/src/node/plugins/index.ts

@@ -77,6 +77,7 @@ export async function resolvePlugins(
     jsonPlugin(
       {
         namedExports: true,
+        stringify: 'auto',
         ...config.json,
       },
       isBuild,

packages/vite/src/node/plugins/json.ts

@@ -6,7 +6,7 @@
  * https://github.com/rollup/plugins/blob/master/LICENSE
  */
 
-import { dataToEsm } from '@rollup/pluginutils'
+import { dataToEsm, makeLegalIdentifier } from '@rollup/pluginutils'
 import { SPECIAL_QUERY_RE } from '../constants'
 import type { Plugin } from '../plugin'
 import { stripBomTag } from '../utils'
@@ -19,10 +19,11 @@ export interface JsonOptions {
   namedExports?: boolean
   /**
    * Generate performant output as JSON.parse("stringified").
-   * Enabling this will disable namedExports.
-   * @default false
+   *
+   * When set to 'auto', the data will be stringified only if the data is bigger than 10kB.
+   * @default 'auto'
    */
-  stringify?: boolean
+  stringify?: boolean | 'auto'
 }
 
 // Custom json filter for vite
@@ -47,24 +48,53 @@ export function jsonPlugin(
       json = stripBomTag(json)
 
       try {
-        if (options.stringify) {
-          if (isBuild) {
+        if (options.stringify !== false) {
+          if (options.namedExports) {
+            const parsed = JSON.parse(json)
+            if (typeof parsed === 'object' && parsed != null) {
+              const keys = Object.keys(parsed)
+
+              let code = ''
+              let defaultObjectCode = '{\n'
+              for (const key of keys) {
+                if (key === makeLegalIdentifier(key)) {
+                  code += `export const ${key} = ${serializeValue(parsed[key])};\n`
+                  defaultObjectCode += `  ${key},\n`
+                } else {
+                  defaultObjectCode += `  ${JSON.stringify(key)}: ${serializeValue(parsed[key])},\n`
+                }
+              }
+              defaultObjectCode += '}'
+
+              code += `export default ${defaultObjectCode};\n`
+              return {
+                code,
+                map: { mappings: '' },
+              }
+            }
+          }
+
+          if (
+            options.stringify === true ||
+            // use 10kB as a threshold
+            // https://v8.dev/blog/cost-of-javascript-2019#:~:text=A%20good%20rule%20of%20thumb%20is%20to%20apply%20this%20technique%20for%20objects%20of%2010%20kB%20or%20larger
+            (options.stringify === 'auto' && json.length > 10 * 1000)
+          ) {
+            // during build, parse then double-stringify to remove all
+            // unnecessary whitespaces to reduce bundle size.
+            if (isBuild) {
+              json = JSON.stringify(JSON.parse(json))
+            }
+
             return {
-              // during build, parse then double-stringify to remove all
-              // unnecessary whitespaces to reduce bundle size.
-              code: `export default JSON.parse(${JSON.stringify(
-                JSON.stringify(JSON.parse(json)),
-              )})`,
+              code: `export default JSON.parse(${JSON.stringify(json)})`,
               map: { mappings: '' },
             }
-          } else {
-            return `export default JSON.parse(${JSON.stringify(json)})`
           }
         }
 
-        const parsed = JSON.parse(json)
         return {
-          code: dataToEsm(parsed, {
+          code: dataToEsm(JSON.parse(json), {
             preferConst: true,
             namedExports: options.namedExports,
           }),
@@ -81,6 +111,20 @@ export function jsonPlugin(
   }
 }
 
+function serializeValue(value: unknown): string {
+  const valueAsString = JSON.stringify(value)
+  // use 10kB as a threshold
+  // https://v8.dev/blog/cost-of-javascript-2019#:~:text=A%20good%20rule%20of%20thumb%20is%20to%20apply%20this%20technique%20for%20objects%20of%2010%20kB%20or%20larger
+  if (
+    typeof value === 'object' &&
+    value != null &&
+    valueAsString.length > 10 * 1000
+  ) {
+    return `JSON.parse(${JSON.stringify(valueAsString)})`
+  }
+  return valueAsString
+}
+
 export function extractJsonErrorPosition(
   errorMessage: string,
   inputLength: number,

packages/vite/src/node/server/index.ts

@@ -539,7 +539,13 @@ export async function _createServer(
       url: string,
       originalCode = code,
     ) {
-      return ssrTransform(code, inMap, url, originalCode, server.config)
+      return ssrTransform(code, inMap, url, originalCode, {
+        json: {
+          stringify:
+            config.json?.stringify === true &&
+            config.json.namedExports !== true,
+        },
+      })
     },
     // environment.transformRequest and .warmupRequest don't take an options param for now,
     // so the logic and error handling needs to be duplicated here.

packages/vite/src/node/server/transformRequest.ts

@@ -408,14 +408,15 @@ async function loadAndTransform(
   if (environment._closing && environment.config.dev.recoverable)
     throwClosedServerError()
 
+  const topLevelConfig = environment.getTopLevelConfig()
   const result = environment.config.dev.moduleRunnerTransform
-    ? await ssrTransform(
-        code,
-        normalizedMap,
-        url,
-        originalCode,
-        environment.getTopLevelConfig(),
-      )
+    ? await ssrTransform(code, normalizedMap, url, originalCode, {
+        json: {
+          stringify:
+            topLevelConfig.json?.stringify === true &&
+            topLevelConfig.json.namedExports !== true,
+        },
+      })
     : ({
         code,
         map: normalizedMap,

playground/json/__tests__/ssr/json-ssr.spec.ts

@@ -11,7 +11,10 @@ beforeEach(async () => {
 test('load json module', async () => {
   await untilUpdated(
     () => page.textContent('.fetch-json-module pre'),
-    'export default JSON.parse("{\\n  \\"hello\\": \\"hi\\"\\n}\\n")',
+    'export const hello = "hi";\n' +
+      'export default {\n' +
+      '  hello,\n' +
+      '};\n',
   )
 })