EC
TS2399
TypeScriptERRORNotableTypeHIGH confidence

Duplicate identifier '_this'. Compiler uses variable declaration '_this' to c...

Production Risk

Build will fail; resolve before shipping.

What this means

A type-checking error (TS2399): Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference.. This diagnostic is emitted by the TypeScript compiler when duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference..

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

TypeScript compiler reports TS2399 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS2399
// Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference.

expected output

error TS2399: Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference.

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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