error TS1259: Module '...express/index' can only be default-imported using the 'allowSyntheticDefaultImports' flag is reported for import express from "express" when the package is CommonJS (its types use export =) and the config does not allow treating module.exports as a default export. The flag named in the message is the one to turn on.
A file named jsconfig.json turns allowSyntheticDefaultImports on by default, and module: "nodenext" implies esModuleInterop, so JavaScript projects mostly meet this error in a tsconfig.json with allowJs, or in a config that switches the default off. The example does the latter.
At a glance
| Code | TS1259 |
|---|---|
| Message | Module '{0}' can only be default-imported using the '{1}' flag |
| TypeScript's category | error |
| Listed under | Modules and imports |
| Turned off by | esModuleInterop, allowSyntheticDefaultImports |
| Depends on | module |
| In .js files | Reported when the file is checked: checkJs in jsconfig.json, or // @ts-check at the top of the file |
The message is TypeScript's own text from its diagnostic messages file (Apache-2.0); {0} and {1} are filled in by tsc for each error.
What it looks like
import express from "express";error TS1259: Module '"/project/node_modules/@types/express/index"' can only be default-imported using the 'allowSyntheticDefaultImports' flag
export const app = express();jsconfig.json for this example
{
"compilerOptions": {
"checkJs": true,
"noEmit": true,
"strict": true,
"target": "es2022",
"module": "esnext",
"types": ["node"],
"moduleResolution": "bundler",
"allowSyntheticDefaultImports": false
},
"include": ["*.js"]
}What causes it
- The imported package is CommonJS and its types say
export =(Express, many older packages). - Neither
esModuleInteropnorallowSyntheticDefaultImportsis on, andmoduleis notnode16tonodenext(which imply interop).
How to fix it
Turn on esModuleInterop
"esModuleInterop": true makes default imports of CommonJS modules work the way Node.js and bundlers run them, and implies allowSyntheticDefaultImports. With module: "nodenext" it is already on.
import express from "express";
export const app = express();jsconfig.json for this example
{
"compilerOptions": {
"checkJs": true,
"noEmit": true,
"strict": true,
"target": "es2022",
"module": "esnext",
"types": ["node"],
"moduleResolution": "bundler",
"esModuleInterop": true
},
"include": ["*.js"]
}Under TypeScript 6.0 and 7.0
Every example on this page also runs under TypeScript 6.0.3 and 7.0.2 when this site is built. One of them reports something different from 5.9.3, the version the page describes; the ✗ on its badge links to its entry below.
allowSyntheticDefaultImports: false is deprecated, then removed
The pattern: A config that sets allowSyntheticDefaultImports (or esModuleInterop) to false, and a default import of a CommonJS package such as Express.
Why: Per the 6.0 release notes these options can no longer be false: 6.0 reports the setting as deprecated (TS5107) and still applies it, so the default import keeps its TS1259; 7.0 reports it as removed (TS5108) and always uses the safer interop, so the default import works and TS1259 is gone. Source: TypeScript 6.0 release notes: Deprecated: --esModuleInterop false and --allowSyntheticDefaultImports false.
A default import of a CommonJS package with synthetic defaults off server.js
- TypeScript 5.9.3
server.js(2,8): error TS1259: Module '"/project/node_modules/@types/express/index"' can only be default-imported using the 'allowSyntheticDefaultImports' flag
- TypeScript 6.0.3differs from 5.9.3
error TS5107: Option 'allowSyntheticDefaultImports=false' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error. server.js(2,8): error TS1259: Module '"/project/node_modules/@types/express/index"' can only be default-imported using the 'allowSyntheticDefaultImports' flag
- TypeScript 7.0.2differs from 5.9.3
jsconfig.json(10,37): error TS5108: Option 'allowSyntheticDefaultImports=false' has been removed. Please remove it from your configuration.
What works in every version: Remove the option (or set esModuleInterop: true) and keep the default import.
The example The same import with esModuleInterop on on this page shows it, with the same result under every version.
Gotchas
import * as express from "express"also passes the checker without interop, but callingexpress()on a namespace import fails at run time in Node.js's ES modules. Turn interop on instead.- The message names the module by its resolved path (tsc prints the full path; on this site examples live at
/project).
Sources
- TSConfig Reference: esModuleInterop · TypeScript
- TSConfig Reference: allowSyntheticDefaultImports · TypeScript
- diagnosticMessages.json (TypeScript 5.9.3) · TypeScript on GitHub
Last reviewed 20 October 2026.