EC
TS1495
TypeScriptERRORNotableSyntaxHIGH confidence

'X' modifier cannot appear on an 'await using' declaration.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1495): 'X' modifier cannot appear on an 'await using' declaration.. This diagnostic is emitted by the TypeScript compiler when 'X' modifier cannot appear on an 'await using' declaration..

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

TypeScript compiler reports TS1495 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1495
// 'X' modifier cannot appear on an 'await using' declaration.

expected output

error TS1495: 'X' modifier cannot appear on an 'await using' declaration.

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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