EC
TS1378
TypeScriptERRORNotableSyntaxHIGH confidence

Top-level 'await' expressions are only allowed when the 'module' option is se...

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1378): Top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'node18', 'node20', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher.. This diagnostic is emitted by the TypeScript compiler when top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'node18', 'node20', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher..

Why it happens
  1. 1await used outside an async function, or async/await return type mismatch
How to reproduce

TypeScript compiler reports TS1378 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1378
// Top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'node18', 'node20', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher.

expected output

error TS1378: Top-level 'await' expressions are only allowed when the 'module' option is set to 'es2022', 'esnext', 'system', 'node16', 'node18', 'node20', 'nodenext', or 'preserve', and the 'target' option is set to 'es2017' or higher.

Fix

Add 'async' to the containing function

WHEN Using await outside an async function

Add 'async' to the containing function
// Mark the function as async
async function fetchData() {
  const result = await fetch('/api/data');
  return result.json();
}

Why this works

await can only be used inside async functions; the 'async' keyword makes the function return a Promise.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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