add-feature

Add Feature

Add functionality by understanding existing code before writing new code.

Workflow

Locate → Understand → Implement → Integrate → Verify

1. Locate

Find where the feature belongs:

tl parallel "tl structure" "tl entry" "tl example <pattern>"

2. Understand

Before writing a single line:

tl parallel \
  "symbols=tl symbols <file>" \
  "style=tl style" \
  "deps=tl deps <file>" \
  "exports=tl exports <file>"

3. Implement

# Extending an existing file?
tl snippet <function> <file>   # Read just the function you're modifying

# New file?
# Follow conventions from tl style, place per tl structure

# Adding a dependency?
tl npm <package>           # Check size, health, and download stats first

4. Integrate

Wire it into the existing system:

tl parallel \
  "impact=tl impact <modified-file>" \
  "guard=tl guard" \
  "diff=tl diff --breaking"

5. Verify

tl parallel "test=tl run '<test command>'" "testmap=tl test-map <file>"

Decision tree

Feature request → Does similar functionality exist?
  ├─ Yes (extending) → tl example to find the pattern
  │   → tl symbols on target file
  │   → tl snippet on the function to extend
  │   → Implement following the existing pattern
  ├─ Yes (replacing) → tl impact on what you're replacing
  │   → tl exports to check public API surface
  │   → Implement, update all consumers
  └─ No (greenfield) → tl structure for placement
      → tl style for conventions
      → tl entry to understand how it'll be wired in
      → Implement, then tl guard to check integration

Tips

• Always run tl example before implementing — the codebase almost always has a precedent
• Use tl npm before adding any new dependency — check size and health
• Run tl diff --breaking after modifying any file with exports
• For React/frontend projects, also use tl component on main UI files
• If a file is under 150 lines, just read it directly — tokenlean overhead isn't worth it