noUnassignedVariables

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JavaScript (and super languages)

Summary

Rule available since: v2.1.0
Diagnostic Category: lint/nursery/noUnassignedVariables
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as no-unassigned-vars

Description

Disallow let or var variables that are read but never assigned.

This rule flags let or var declarations that are never assigned a value but are still read or used in the code. Since these variables will always be undefined, their usage is likely a programming mistake.

Examples

Invalid

1
let status;
2
if (status === 'ready') {
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    console.log('Status is ready');
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}

code-block.js:1:5 lint/nursery/noUnassignedVariables ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The variable ‘status’ is declared but never assigned a value.
  
  > 1 │ let status;
      │     ^^^^^^
    2 │ if (status === ‘ready’) {
    3 │     console.log(‘Status is ready’);
  
  ℹ Variable declared without assignment. Either assign a value or remove the declaration.

1
let value: number | undefined;
2
console.log(value);

code-block.ts:1:5 lint/nursery/noUnassignedVariables ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ The variable ‘value’ is declared but never assigned a value.
  
  > 1 │ let value: number | undefined;
      │     ^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ console.log(value);
    3 │ 
  
  ℹ Variable declared without assignment. Either assign a value or remove the declaration.

Valid

1
let message = "hello";
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console.log(message);
3

4
let user;
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user = getUser();
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console.log(user.name);
7

8
let count;
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count = 0;
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count++;

1
declare let value: number | undefined;
2
console.log(value);
3

4
declare module "my-module" {
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    let value: string;
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    export = value;
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}

How to configure

1
{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUnassignedVariables": "error"
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      }
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    }
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  }
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}