JSPM

Magic number detection for javascript. Let Buddy sniff out the unnamed numerical constants in your code.

Overview

We all know magic numbers are frowned upon as a programming practice. They may give no indication of their meaning, and when used multiple times, can result in future inconsistencies. They can expose you to the risk of typos, hinder maintenance and have an impact on readability. That's where Buddy comes in.

Buddy is a cli tool that's eager to find the magic numbers in your code. It accepts a list of paths to parse, and renders any found instances with the selected reporter. In the case of directories, they're walked recursively, and only .js files are analyzed. Any node_modules dirs are also ignored.

Since const is not widespread in JavaScript, it defaults to searching for numbers which are not the sole literal in an object expression or variable declaration. Furthermore, specific values can be ignored, such as 0 and 1, which are ignored by default.

Who's a good boy?

What are magic numbers?

Magic numbers are unnamed numerical constants, though the term can sometimes be used to refer to other literals as well. Take the following contrived example:

function getTotal(subtotal) {
  var beforeTax = subtotal + 9.99;
  return beforeTax + (beforeTax * 0.13);
}

In the above function, the meaning of the two numbers might not be clear. What is this 9.99 charge? In our case, let's say it's a shipping rate. And what about the 0.13? It's the sales tax. Buddy will highlight those two instances:

$ buddy example.js

example.js:2 | var beforeTax = subtotal + 9.99;
example.js:3 | return beforeTax + (beforeTax * 0.13);

 2 magic numbers found across 1 file

If the tax rate was used in multiple locations, it's prone to human error. And it might not be immediately clear that the 9.99 charge is a flat rate shipping cost, which can affect maintenance. So how would this be improved?

var FLAT_SHIPPING_COST = 9.99;
var SALES_TAX = 0.13;

function getTotal(subtotal) {
  var beforeTax = subtotal + FLAT_SHIPPING_COST;
  return beforeTax + (beforeTax * SALES_TAX);
}

Or, depending on your target platforms or browsers, by using the const keyword for variable declaration instead of var. While const is available in Node, you should take note of its browser compatibility for front end JavaScript.

$ buddy example.js

 No magic numbers found across 1 file

Installation

It can be installed via npm using:

npm install -g buddy.js

If you'd like to use buddy.js with Grunt, take a look at grunt-buddyjs

Usage

Usage: buddy [options] <paths ...>

Options:

  -h, --help                             output usage information
  -V, --version                          output the version number
  -e, --enforce-const                    require literals to be defined using const
  -i, --ignore <numbers>                 list numbers to ignore (default: 0,1)
  -I, --disable-ignore                   disables the ignore list
  -r, --reporter [simple|detailed|json]  specify the reporter to use (default: simple)
  -C, --no-color                         disables colors