tessl/npm-lebab

JavaScript ES5 to ES6/ES7 transpiler that performs the opposite function of Babel

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Impact

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Overview

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Files

CLI Usage

Name: tessl/npm-lebab
Author: tessl

Lebab provides a comprehensive command-line interface for transforming JavaScript files in batch operations.

Installation

# Global installation for CLI usage
npm install -g lebab

# Local installation for project-specific usage
npm install lebab

Capabilities

Basic File Transformation

Transform a single file with specified transforms.

# Basic syntax
lebab <input-file> -o <output-file> --transform <transforms>

# Examples
lebab es5.js -o es6.js --transform let
lebab old-code.js -o modern-code.js --transform let,arrow,arrow-return

In-Place Directory Transformation

Transform all files in a directory or matching a pattern.

# Transform all .js files in directory
lebab --replace src/js/ --transform arrow

# Transform with specific glob patterns  
lebab --replace 'src/js/**/*.jsx' --transform arrow
lebab --replace 'lib/**/*.js' --transform let,arrow

# Transform multiple file types
lebab --replace 'src/**/*.{js,jsx}' --transform class,commonjs

Transform Options

Specify which transformations to apply.

# Single transform
--transform let
-t let

# Multiple transforms (comma-separated)
--transform let,arrow,arrow-return
-t class,template,obj-shorthand

# All safe transforms
--transform arrow,arrow-return,for-of,for-each,arg-rest,arg-spread,obj-method,obj-shorthand,no-strict,exponent,multi-var

# Common unsafe transforms  
--transform let,class,commonjs,template,default-param

Command Options

# Show help
lebab --help
lebab -h

# Show version
lebab --version  
lebab -v

# Input/output options
--out-file <file>    # Specify output file
-o <file>            # Alias for --out-file

--replace <pattern>  # In-place transformation with glob pattern
-r <pattern>         # Alias for --replace

--transform <list>   # Comma-separated transform names
-t <list>           # Alias for --transform

Usage Examples

Modernizing Legacy Code

# Start with safe transforms
lebab --replace 'src/**/*.js' --transform arrow,arrow-return,obj-method,obj-shorthand

# Add variable declarations
lebab --replace 'src/**/*.js' --transform let

# Convert to classes (review output carefully)
lebab --replace 'src/**/*.js' --transform class

# Convert to ES6 modules (review imports/exports)  
lebab --replace 'src/**/*.js' --transform commonjs

Step-by-Step Modernization

# Step 1: Safe syntax improvements
lebab old-app.js -o step1.js --transform arrow,obj-method,obj-shorthand

# Step 2: Variable declarations  
lebab step1.js -o step2.js --transform let

# Step 3: Template literals
lebab step2.js -o step3.js --transform template

# Step 4: Modern features
lebab step3.js -o modern-app.js --transform default-param,arg-spread,includes

Processing Specific Frameworks

# React components
lebab --replace 'src/components/**/*.jsx' --transform let,arrow,class,obj-method

# Node.js modules  
lebab --replace 'lib/**/*.js' --transform let,arrow,commonjs,template

# Express.js applications
lebab --replace 'routes/**/*.js' --transform let,arrow,default-param,arg-spread

Output and Warnings

The CLI provides detailed feedback about the transformation process:

# Example output with warnings
$ lebab problematic.js -o result.js --transform let

problematic.js:
5:  warning  Unable to transform var  (let)
12: warning  Variable used before declaration  (let)

# Successful transformation
$ lebab simple.js -o result.js --transform arrow

# No output indicates successful transformation

Warning Types

Common warning messages and their meanings:

Unable to transform var (let) - Variable cannot be safely converted to let/const
Variable used before declaration (let) - Temporal dead zone issues
Cannot convert to arrow function (arrow) - Function uses this or arguments
Potential prototype conflict (class) - Class conversion may affect prototype chain

Best Practices

Recommended Workflow

Start with safe transforms - Apply low-risk transforms first
One transform at a time - Apply transforms individually to review changes
Test thoroughly - Run tests after each transformation
Review diffs - Manually inspect all changes, especially for unsafe transforms
Version control - Commit between transformation steps

Transform Order Recommendations

# Recommended order for comprehensive modernization
lebab --replace 'src/**/*.js' --transform multi-var    # 1. Split declarations
lebab --replace 'src/**/*.js' --transform obj-shorthand # 2. Object syntax
lebab --replace 'src/**/*.js' --transform obj-method   # 3. Method syntax  
lebab --replace 'src/**/*.js' --transform let          # 4. Variable declarations
lebab --replace 'src/**/*.js' --transform arrow        # 5. Arrow functions
lebab --replace 'src/**/*.js' --transform arrow-return # 6. Concise arrows
lebab --replace 'src/**/*.js' --transform class        # 7. ES6 classes
lebab --replace 'src/**/*.js' --transform template     # 8. Template literals
lebab --replace 'src/**/*.js' --transform commonjs     # 9. ES6 modules (last)

Error Prevention

# Always backup before in-place transforms
cp -r src src-backup
lebab --replace 'src/**/*.js' --transform let

# Use version control
git add -A
git commit -m "Before lebab transformation"
lebab --replace 'src/**/*.js' --transform arrow
git diff  # Review changes