noUselessParameterPropertyAssignment (JavaScript)

Language JavaScript (and super languages)

Summary

Diagnostic Category: lint/nursery/noUselessParameterPropertyAssignment
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as @typescript-eslint/no-unnecessary-parameter-property-assignment

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUselessParameterPropertyAssignment": "error"
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      }
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    }
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  }
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}

Description

Disallow assigning a parameter property to itself in the constructor.

A parameter property is a constructor parameter marked with public, protected, private, readonly, or override. TypeScript creates a class property with the same name and sets it to the parameter’s value before the constructor body runs.

Writing this.name = name in the constructor body sets the property to the value it already has. The line does nothing and can be removed.

The rule doesn’t report the assignment if the parameter or the property is changed before it, because then the assignment can change the value of the property.

Examples

Invalid

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class User {
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    constructor(public name: string) {
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        this.name = name;
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    }
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}

code-block.ts:3:9 lint/nursery/noUselessParameterPropertyAssignment ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This assignment sets the property to the value it already has.
  
    1 │ class User {
    2 │     constructor(public name: string) {
  > 3 │         this.name = name;
      │         ^^^^^^^^^^^^^^^^
    4 │     }
    5 │ }
  
  ℹ The parameter property already sets this property to the parameter's value before the constructor body runs.
  
  ℹ Remove the assignment.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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class User {
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    constructor(private readonly id?: string) {
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        this.id ??= id;
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    }
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}

code-block.ts:3:9 lint/nursery/noUselessParameterPropertyAssignment ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This assignment sets the property to the value it already has.
  
    1 │ class User {
    2 │     constructor(private readonly id?: string) {
  > 3 │         this.id ??= id;
      │         ^^^^^^^^^^^^^^
    4 │     }
    5 │ }
  
  ℹ The parameter property already sets this property to the parameter's value before the constructor body runs.
  
  ℹ Remove the assignment.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

Valid

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class User {
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    constructor(public name: string) {}
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}
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class Label {
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    constructor(public text: string) {
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        text = text.trim();
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        this.text = text;
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    }
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}
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class Point {
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    x: number;
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    constructor(x: number) {
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        this.x = x;
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    }
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}