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dale-chall-formula

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

Contents

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]).

ScoreCorresponding grade levelReturn value
Less than 5Grade 4 and lower[0, 4]
Less than 6Grades 5 and 6[5, 6]
Less than 7Grades 7 and 8[7, 8]
Less than 8Grades 9 and 10[9, 10]
Less than 9Grades 11 and 12[11, 12]
Less than 10Grades 13 and 15 (College)[13, 15]
HigherGrades 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

Contribute

Yes please! See How to Contribute to Open Source.

Security

This package is safe.

License

MIT © Titus Wormer

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