Code Refactoring

Regex is invaluable for large-scale code refactoring. Whether you're renaming variables, updating import statements, or migrating APIs, these patterns will help.

Variable and Function Renaming

Simple Rename

Find all occurrences of a variable name (as a whole word):

\boldName\b

The \b word boundaries ensure you match oldName but not oldNameSuffix or prefixOldName.

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Rename with Context

Find variable declarations specifically:

\b(const|let|var)\s+oldName\b

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Rename Object Property Access

\.oldProperty\b

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Import Statement Updates

ES6 Import Refactoring

Find imports from a specific module:

import\s+(?:{[^}]+}|\w+)\s+from\s+['"]@old-package['"]

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Extract Named Imports

import\s+{\s*(?<imports>[^}]+)\s*}\s+from\s+['"](?<module>[^'"]+)['"]

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CommonJS to ES6

Find require statements to convert:

const\s+(?<name>\w+)\s*=\s*require\(['"](?<module>[^'"]+)['"]\)

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API Migration

Update Method Calls

Migrate from old API to new:

oldApi\.oldMethod\(([^)]*)\)

Replace with: newApi.newMethod($1)

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Update Callback to Promise

Find callback-style code:

(\w+)\(([^,]+),\s*function\s*\((?:err,\s*)?(\w+)\)\s*{

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React Class to Hooks

Find this.state references:

this\.state\.(\w+)

Find this.setState:

this\.setState\(\{([^}]+)\}\)

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String and Comment Updates

Update String Literals

Find strings containing specific text:

(['"`])([^'"`]*old-text[^'"`]*)\1

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Find TODO Comments

\/\/\s*TODO:?\s*(.*)

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Find FIXME and HACK Comments

\/\/\s*(TODO|FIXME|HACK|XXX):?\s*(.*)

Type Annotations

TypeScript Type Updates

Find type annotations:

:\s*OldType\b

Find generic type parameters:

<OldType(?:\s*,\s*\w+)*>

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Find Interface Properties

(\w+):\s*OldType;

Practical Workflow

Step-by-Step Refactoring

1. Write the pattern in RegexLens
2. Test with samples from your actual codebase
3. Check the explanation to ensure it matches what you expect
4. Review warnings for potential issues
5. Run find-and-replace in your IDE
6. Run tests to verify the refactoring

IDE Integration

Most IDEs support regex find-and-replace:

• VS Code: Ctrl/Cmd + H, click .* to enable regex
• IntelliJ: Ctrl/Cmd + R, check "Regex" checkbox
• Sublime Text: Ctrl/Cmd + H, enable regex mode

Capture Groups for Replacement

Use capture groups to preserve parts of the match:

Find:

console\.log\((['"`][^'"`]+['"`])\)

Replace:

logger.info($1)

This converts console.log('message') to logger.info('message').

Common Refactoring Patterns