follows-order

Checks that specific array elements or string characters appear only in a certain order. Packaged as a Node.js module.

Installation

npm install follows-order --save

The module exposes a single function.

Usage

Array Example

const followsOrder = require('follows-order')

const data = {
  name: "Test",
  description: "This is a test",
  module: "follows-order",
}

// Check to make sure that `name` precedes `description`.
// (Note: JavaScript does not guarantee object key order.
// This is only for the sake of example.)
followsOrder(Object.keys(data), ['name', 'description']) // true

String Example

const followsOrder = require('follows-order')

const data = 'test'

// Does the first "t" come before the first "e"?
followsOrder(data, 'te') // true

A Note on Duplicates

If an array or string is being checked to see if its order follows [A, B], then the first B cannot appear before the first A does, even if the [A, B] pattern occurs later.

This is according to design: the module is made to enforce a certain order, not merely check for a pattern.

Data	Order	Result	Reason
[B,A,B]	[A,B]	Fail	The first instance of A should have preceded the first instance of B.
[A,B,B,A]	[A,B]	Pass	A and B only occur once in the order, so only the first instances in the data are checked.
[A,B,B,A]	[A,B,A,B]	Fail	A and B occur twice in the order, so the second A in the data should have preceded the second B.

const followsOrder = require('follows-order')

const data = [1, 2, 1]

followsOrder(data, [1, 2]) // true
followsOrder(data, [2, 1]) // false, because in the data the first instance of 1 occurs before 2
followsOrder(data, [1, 2, 1]) // true

If you don’t want to deal with duplicate elements in your data, you’ll need to deduplicate the data yourself before you check it with follows-order.