dale-chall-formula

Formula to detect the grade level of text according to the (revised) Dale–Chall readability formula.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • daleChallFormula(counts)
  • daleChallGradeLevel(score)
• Types
• Compatibility
• Related
• Contribute
• Security
• License

What is this?

This package exposes an algorithm to detect ease of reading of English texts.

When should I use this?

You’re probably dealing with natural language, and know you need this, if you’re here!

See dale-chall for a list of words which count as “familiar”. All other words are considered “difficult” for this algorithm.

Install

This package is ESM only. In Node.js (version 14.14+, 16.0+), install with npm:

npm install dale-chall-formula

In Deno with esm.sh:

import {daleChallFormula, daleChallGradeLevel} from 'https://esm.sh/dale-chall-formula@2'

In browsers with esm.sh:

<script type="module">
  import {daleChallFormula, daleChallGradeLevel} from 'https://esm.sh/dale-chall-formula@2?bundle'
</script>

Use

import {daleChallFormula, daleChallGradeLevel} from 'dale-chall-formula'

daleChallFormula({word: 30, sentence: 2, difficultWord: 6}) // => 4.41208

daleChallGradeLevel(daleChallFormula({word: 30, sentence: 2, difficultWord: 6})) // => [9, 10]

API

This package exports the identifiers daleChallFormula, daleChallGradeLevel. There is no default export.

daleChallFormula(counts)

Given the number of words (word), the number of sentences (sentence), and the number of unique unfamiliar words in a document (difficultWord), returns the score associated with the document.

counts

Counts from input document.

counts.sentence

Number of sentences (number, required).

counts.word

Number of words (number, required).

counts.difficultWord

Number of unique unfamiliar words (number, default: 0).

Returns

Score representing ease of reading (number).

Pass it to daleChallGradeLevel to get grade levels.

daleChallGradeLevel(score)

Turn a dale–chall score into U.S. grade levels.

score

Score representing ease of reading.

Returns

Grade levels ([number, number]).

Score	Corresponding grade level	Return value
Less than 5	Grade 4 and lower	[0, 4]
Less than 6	Grades 5 and 6	[5, 6]
Less than 7	Grades 7 and 8	[7, 8]
Less than 8	Grades 9 and 10	[9, 10]
Less than 9	Grades 11 and 12	[11, 12]
Less than 10	Grades 13 and 15 (College)	[13, 15]
Higher	Grades 16 and higher (College Graduate)	[16, Infinity]

Types

This package is fully typed with TypeScript. It exports the additional type Counts.

Compatibility

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 14.14+ and 16.0+. It also works in Deno and modern browsers.

Related

• automated-readability — uses character count instead of error-prone syllable parser
• coleman-liau — uses letter count instead of an error-prone syllable parser
• flesch — uses syllable count
• flesch-kincaid — like flesch-formula, returns U.S. grade levels
• gunning-fog — uses syllable count, needs POS-tagging and NER
• smog-formula — like gunning-fog-index, without needing advanced NLP
• spache-formula — uses a dictionary, suited for lower reading levels

Contribute

Yes please! See How to Contribute to Open Source.

Security

This package is safe.

License

MIT © Titus Wormer