Always return empty arrays in Typescript

typescriptreact
When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }

Install this rule for wispbit

Quick Install

Recommended
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Run this one command to automatically install the rule:

curl -fsSL https://wispbit.com/api/install?rule=typescript-always-return-empty | bash

Manual install

1

Copy the rule

---
include: *.ts,*.tsx
---
When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```
2

Add the rule into your project

Save the copied content as: .wispbit/rules/typescript-always-return-empty.md

Install this rule for Coderabbit

Copy the configuration below and add it to your repository as .coderabbit.yml in your project root.

reviews:
  path_instructions:
    - path: "*.ts,*.tsx"
      instructions: |
                
        When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
        
        Bad:
        
        ```typescript
        function getUserNames(): string[] | undefined {
          if (users.length === 0) {
            return undefined
          }
          return users.map((user) => user.name)
        }
        ```
        
        Good:
        
        ```typescript
        function getUserNames(): string[] {
          if (users.length === 0) {
            return []
          }
          return users.map((user) => user.name)
        }
        ```

Install this rule for Greptile

Greptile rules can be added through the web interface. Please see this documentation for details on how to add custom rules and context.

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

File Path Patterns:

*.ts
*.tsx

Install this rule for GitHub Copilot

Copilot instructions can be added through the interface. See the documentation for details on how to create coding guidelines.

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

File Path Patterns:

*.ts
*.tsx

Install this rule for Graphite Diamond

Diamond custom rules can be added through the interface. See the documentation for details on how to create custom rules.

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

File Path Patterns:

*.ts
*.tsx

Use with Cline

Copy the rule below and ask Cline to review your code using this rule

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

Use with OpenAI Codex

Copy the rule below and ask OpenAI Codex to review your code using this rule

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

Use with Cursor

Copy the rule below and ask Cursor to review your code using this rule

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```

Use with Claude Code

Copy the rule below and ask Claude Code to review your code using this rule

When defining methods that return collections like arrays, always return an empty array instead of undefined when no items exist.
Bad:
```typescript
function getUserNames(): string[] | undefined {
  if (users.length === 0) {
    return undefined
  }
  return users.map((user) => user.name)
}
```
Good:
```typescript
function getUserNames(): string[] {
  if (users.length === 0) {
    return []
  }
  return users.map((user) => user.name)
}
```