check-constants

Find numbers and strings that should be extracted as a declaration statement

The idea behind this project is that numbers and strings should be extracted as declared constants (or vars), so that they could be easily controlled & changed. Imagine that you have a function which will calculate the total sum owed after taxes:

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

As you can see, in a month from now, and in a large code base, we might not remember what are those 9.99 and 0.13, and also, suppose we have several instances of the number 0.13 and we want to change it? Now you need to refactor all occurrences hoping you didn't miss anything or over-do it.

check-constants will find the numbers that you should extract as a declaration statement:

The example above, could be re-factored to:

//corrected.js
 
var FIXED_COST = 9.99;
var TAX = 0.13;
 
function getTotal(subtotal) {
    var beforeTax = subtotal + FIXED_COST;
    return beforeTax + (beforeTax * TAX);
}

Now let's see what happens when we run check-constants on the corrected file:

This project uses Rocambole to parse your JS, and it's a simplified version of buddy.js which I found overcomplicated and too heavy.

Usage

Command Line

Installation

$ npm install --global check-constants

Examples

# show the help menu 
❯ check-constants --help
 
  Usage: check-constants [options] <file ...>
 
  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
    -s, --strings                 check strings as well
    -m, --min-length [minLength]  minimum length of strings to be checked [0]
    -r, --reporter [reporter]     specify the reporter to use [table|json] (default: table)
 
  Examples:
 
    $ check-constants index.js
    $ check-constants --reporter json index.js
    $ cat index.js | check-constants
 
# Easily check a file by path 
$ check-constants file.js
 
# Check files by using glob pattern 
$ check-constants js/**/*.js
 
# Check a file by piping it 
$ cat file.js | check-constants
 
# Format output as json 
$ check-constants file.js --reporter json
 
# Override ignored numbers 
$ check-constants file.js --ignore 1,5,13
 
# Disable default ignored numbers (0,1) 
$ check-constants file.js --disable-ignore
 
# Make sure variables are declared as const 
$ check-constants --enforce-const file.js
 
# Check the current version of the cli app 
$ check-constants --version

Programmatic

Installation

$ npm install --save-dev check-constants

Examples

var fs = require('fs');
var checkConstants = require('check-constants');
var options = {};
 
var contents = fs.readFileSync('./contents.js', 'utf8');
var errors = checkConstants.inspect(contents, options);
// -> errors will contain possible variables that need extraction

Build Time

check-constants can also be used in conjunction with other javascript build systems, such as:

• gulp-check-constants
• grunt-check-constants

The Output

[{
    "file": "index.js",
    "code": "i = i + 2",
    "value": 2,
    "loc": {
        "start": {
            "line": 5,
            "column": 28
            },
        "end": {
            "line": 5,
            "column": 29
            }
        }
}]

API

check-constants exposes the following API:

.inspect(contents, options)

contents

String - the contents to check

options

Options is an optional object containing the following properties:

strings

Type: Boolean

Default: false

Whether to check for strings as well as numbers.

minLength

Type: Number

Default: 0

Only used when option strings is true. Limits the minimum string length checking.

enforceConst

Type: Boolean

Default: false

Whether to enforce declarations to be used with const.

ignore

Type: Array

Default: [0, 1]

Strings and numbers to ignore

file

Type: String

Default: null

Filename being checked if available (i.e not from a stream). Will be attached to the result object.

.log[reporter](results)

reporter

Which reporter to use. Currently supported json and table.

results

The resulting object from .inspect()

License

MIT ©Gilad Peleg