EC
TS17020
TypeScriptERRORNotableTypeHIGH confidence

'X' at the start of a type is not valid TypeScript syntax. Did you mean to wr...

Production Risk

Build will fail; resolve before shipping.

What this means

A TypeScript diagnostic (TS17020): 'X' at the start of a type is not valid TypeScript syntax. Did you mean to write 'X'?. This diagnostic is emitted by the TypeScript compiler when 'X' at the start of a type is not valid TypeScript syntax. Did you mean to write 'X'?.

Why it happens
  1. 1Incorrect TypeScript syntax or type usage
  2. 2Type mismatch between declared and actual value
How to reproduce

TypeScript compiler reports TS17020 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS17020
// 'X' at the start of a type is not valid TypeScript syntax. Did you mean to write 'X'?

expected output

error TS17020: 'X' at the start of a type is not valid TypeScript syntax. Did you mean to write 'X'?

Fix

Address the TypeScript diagnostic

WHEN When this error is reported by the compiler

Address the TypeScript diagnostic
// Run the TypeScript compiler for details:
npx tsc --noEmit
// Use the TypeScript playground to test your code:
// https://www.typescriptlang.org/play

Why this works

Review the full error message and location; the TypeScript handbook provides guidance on each error category.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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