Matthew C.
—When using the TypeScript compiler to create JavaScript files from TypeScript files, in a process known as transpiling, you may get the following error in your terminal:
This module is declared with 'export =', and can only be used with a default import when using the 'esModuleInterop' flag.
This error occurs when the TypeScript config esModuleInterop
flag either isn’t set or is set to false
, and a non-ES module package is imported, by default, in an ES module file.
TypeScript treats CommonJS, AMD, and UMD modules similarly to how it treats ES modules. This can cause issues with importing modules from CommonJS modules into ES modules, as there may be inconsistencies with the default export type. The default
export is the exports
object from Node version 14.13.0. However, different JavaScript bundlers may use exports.default
as the default export.
Set the esModuleInterop
flag to true
in your tsconfig.json
file. Its default value is true
if the TypeScript config option module
is node16
or nodenext
.
Setting the esModuleInterop
flag to true
in your tsconfig.json
file also adds extra interoperability code to the transpiled JavaScript to handle different types of default imports from CommonJS modules.
However, you may have esModuleInterop
set to true
but still find that you get the error when you run the tsc
command and specify the input file as follows:
tsc server.ts
This is because when you specify input files, tsconfig.json
files are ignored.
Next, set the output folder for the transpiled JavaScript:
"outDir": "./dist",
Transpile using the tsc
command and run the transpiled JavaScript code:
tsc && node ./dist/server.js
You can also use Nodemon to transpile and run your TypeScript code. It automatically restarts your Node.js application when file changes are detected:
nodemon ./server.ts
Nodemon version 1.19 added inbuilt support for TypeScript files. It uses ts-node to run your Node.js application.
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