EC
TS2582
TypeScriptERRORNotableTypeHIGH confidence

Cannot find name 'X'. Do you need to install type definitions for a test runn...

Production Risk

Build will fail; resolve before shipping.

What this means

A type-checking error (TS2582): Cannot find name 'X'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`.. This diagnostic is emitted by the TypeScript compiler when cannot find name 'X'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`..

Why it happens
  1. 1The variable, type, or namespace is not declared in scope
  2. 2A missing import or type declaration
How to reproduce

TypeScript compiler reports TS2582 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS2582
// Cannot find name 'X'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`.

expected output

error TS2582: Cannot find name 'X'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha`.

Fix

Declare or import the missing name

WHEN When a variable or type is not in scope

Declare or import the missing name
// Add the missing import
import { MyType } from './my-module';
// Or declare the variable
const myVar: MyType = ...;

Why this works

TypeScript requires all names to be declared before use; add the missing declaration or import.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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