JS with Types Start

TypeScript error

TS6133: A variable, import or parameter that is never read

  • Error TS6133
  • Reported with noUnusedLocals
  • Reported with noUnusedParameters
  • Tested with TypeScript 5.9

error TS6133: 'count' is declared but its value is never read. is reported, with noUnusedLocals on, for imports, variables, functions and private class members that nothing reads, and with noUnusedParameters on, for parameters. Neither option is part of strict.

With both options off the checker still notices: editors that run TypeScript's language service show the same names faded out, as a suggestion rather than an error, and tsc prints nothing.

At a glance

CodeTS6133
Message'{0}' is declared but its value is never read.
TypeScript's categoryerror
Listed underClasses, JSX and unused code
Turned on by noUnusedLocals, noUnusedParameters
In .js files Reported when the file is checked: checkJs in jsconfig.json, or // @ts-check at the top of the file

The message is TypeScript's own text from its diagnostic messages file (Apache-2.0); {0} is filled in by tsc for each error.

What it looks like

report.js Error confirmed 5.9.3 TypeScript 5.9.3, run 21 October 2026: report.js(2,1): error TS6133: 'readFile' is declared but its value is never read. report.js(9,35): error TS6133: 'currency' is declared but its value is never read. report.js(11,9): error TS6133: 'count' is declared but its value is never read. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. report.js(2,1): error TS6133: 'readFile' is declared but its value is never read. report.js(9,35): error TS6133: 'currency' is declared but its value is never read. report.js(11,9): error TS6133: 'count' is declared but its value is never read. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. report.js(2,10): error TS6133: 'readFile' is declared but its value is never read. report.js(9,35): error TS6133: 'currency' is declared but its value is never read. report.js(11,9): error TS6133: 'count' is declared but its value is never read. checked 21 October 2026 
import { readFile } from "node:fs/promises";error TS6133: 'readFile' is declared but its value is never read.

/**
 * @param {number[]} totals
 * @param {string} currency
 */
export function summarize(totals, currency) {error TS6133: 'currency' is declared but its value is never read.
  const count = totals.length;error TS6133: 'count' is declared but its value is never read.
  return totals.reduce((sum, t) => sum + t, 0);
}
An unused import, variable and parameter.
jsconfig.json for this example 
{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": ["node"],
    "noUnusedLocals": true,
    "noUnusedParameters": true
  },
  "include": ["*.js"]
}

What causes it

  • Code was removed and its import or variable was left behind.
  • A parameter is required by a callback's position but not used ((event, index) => ... using only index).
  • noUnusedLocals or noUnusedParameters is on.

How to fix it

Remove it, or start a parameter's name with _

Delete unused imports and variables. A parameter you must keep for its position can start with an underscore (_currency), which noUnusedParameters skips by design.

report.js TypeScript 5.9.3 TypeScript 5.9.3, run 21 October 2026: No errors. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. No errors. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. No errors. checked 21 October 2026 
/**
 * @param {number[]} totals
 * @param {string} _currency Kept for callers; not used yet.
 */
export function summarize(totals, _currency) {
  return totals.reduce((sum, t) => sum + t, 0);
}
Remove what is unused, or prefix a required parameter with _.
jsconfig.json for this example 
{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": ["node"],
    "noUnusedLocals": true,
    "noUnusedParameters": true
  },
  "include": ["*.js"]
}

Gotchas

  • An import used only in a JSDoc type counts as read. For imports that exist only for types, @import is cleaner: it is a comment, so it adds no import to the running code.
  • Destructuring to drop a property (const { password, ...user } = row) is not reported: unused names next to a rest element are ignored, so this way of removing a property stays clean under noUnusedLocals.

  • jsconfig.json option

    noUnusedLocals and noUnusedParameters

    noUnusedLocals and noUnusedParameters report variables, imports and parameters that are declared and never read (TS6133). A leading _ exempts a parameter.

  • JSDoc tag

    @import

    The JSDoc @import tag (TypeScript 5.5 and later) brings types from another module into a .js file with ES import syntax and nothing imported at run time.

  • jsconfig.json option

    strict

    strict turns on the strict type-checking family with one switch: nine options in TypeScript 5.9. What each catches in a .js file, and how to turn one back off.

  • TypeScript error

    TS2578: A // @ts-expect-error with nothing to expect

    TS2578 means a // @ts-expect-error comment sits above a line that no longer has an error. Remove the comment; that is the directive doing its job.

  • Editor setup

    VS Code

    Set up VS Code for type-checked JavaScript: how it reads jsconfig.json, using the project's TypeScript version, and listing errors in files you have not opened.

Sources

Last reviewed 20 October 2026.