noDynamicDelete (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.5
Diagnostic Category: lint/nursery/noDynamicDelete
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as @typescript-eslint/no-dynamic-delete

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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        "noDynamicDelete": "error"
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      }
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    }
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  }
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}

Description

Disallow using the delete operator with a property name that is computed at runtime.

The delete operator removes a property from an object. When the property name is written inside square brackets and comes from a variable, a function call, or another expression, the code is using a plain object to store a changing set of keys. It is hard to tell which property gets removed just by reading the code.

A Map or a Set is built for this use. Both have a delete() method for removing entries.

This rule allows square brackets that contain a string literal, a number literal, or a negative number literal, because the property name is fixed in the code.

In Node.js, process.env holds the environment variables of the running program, and it can’t be replaced with a Map. The rule still reports delete process.env[name], and suggests deleting each environment variable by its name instead.

Examples

Invalid

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const name = "name";
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delete container[name];

code-block.js:2:18 lint/nursery/noDynamicDelete ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid using delete with a property name that is computed at runtime.
  
    1 │ const name = "name";
  > 2 │ delete container[name];
      │                  ^^^^
    3 │ 
  
  ℹ Removing properties by a changing name makes it hard to tell which property gets removed.
  
  ℹ Use a Map or a Set and call its delete() method instead.
  
  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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delete container[name.toUpperCase()];

code-block.js:1:18 lint/nursery/noDynamicDelete ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid using delete with a property name that is computed at runtime.
  
  > 1 │ delete container[name.toUpperCase()];
      │                  ^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Removing properties by a changing name makes it hard to tell which property gets removed.
  
  ℹ Use a Map or a Set and call its delete() method instead.
  
  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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const variable = "API_KEY";
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delete process.env[variable];

code-block.js:2:20 lint/nursery/noDynamicDelete ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Avoid using delete with an environment variable name that is computed at runtime.
  
    1 │ const variable = "API_KEY";
  > 2 │ delete process.env[variable];
      │                    ^^^^^^^^
    3 │ 
  
  ℹ Removing environment variables by a changing name makes it hard to tell which variables get removed.
  
  ℹ Delete each environment variable by its name instead, for example delete process.env.API_KEY.
  
  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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delete container.aaa;
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delete container[7];
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delete container[-1];
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delete container["aaa"];
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delete container["Infinity"];
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const map = new Map();
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map.delete(name);
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delete process.env.API_KEY;