EC
TS4126
TypeScriptERRORNotableDeclarationHIGH confidence

One value of 'X.X' is the string 'X', and the other is assumed to be an unkno...

Production Risk

Build will fail; resolve before shipping.

What this means

A declaration emit error (TS4126): One value of 'X.X' is the string 'X', and the other is assumed to be an unknown numeric value.. This diagnostic is emitted by the TypeScript compiler when one value of 'X.X' is the string 'X', and the other is assumed to be an unknown numeric value..

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

TypeScript compiler reports TS4126 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS4126
// One value of 'X.X' is the string 'X', and the other is assumed to be an unknown numeric value.

expected output

error TS4126: One value of 'X.X' is the string 'X', and the other is assumed to be an unknown numeric value.

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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