Compute the high-level endpoint impact of tiny code changes

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Express Butterfly Effect 🦋🌊


When a butterfly flaps its wings over some line of your code there is was no telling of the consequence.
express-butterfly-effect takes one or more file changes and gives you back which express endpoints might be affected by those changes


npm i --save-dev express-butterfly-effect


You can either use express-butterfly-effect as a command-line app or as a library.
As a command-line app you would do:
./node_modules/.bin/express-butterfly-effect glob1 [glob2] change1 [change2]

You need to specify at least one glob and one change. Globs are used to find all the .js files in your project.
A change is a path to a file, followed by a : and then a line number or line range (start-count), possibly followed by other : plus line or range.
For example:
./node_modules/.bin/express-butterfly-effect './lib/**/*.js' \
  ./lib/my-file.js:1:4-2:10 \

# my-file.js changed at lines 1, 4, 5 and 10
# my-other-file.js changed at line 5

To use express-butterfly-effect you need to:
const computeEndpointImpact = require('express-butterfly-effect').default;
// Note: .default in the line above!

const impact = computeEndpointImpact(
  globs, // string[],
  targetFiles, // string[]

// impact is a string[], where each item looks like:
// 'get /api/users/1' (i.e. method + ' ' +  path)

Pulling changes from git

./node_modules/express-butterfly-effect/ [base-branch]

If you omit base-branch, the script defaults to master. This script returns the changes in the format you need to pass to express-butterfly-effect.
All together it would look something like:
./node_modules/.bin/express-butterfly-effect \
  './lib/**/*.js' \