Get shields.io badges for jest coverage.

jest-coverage-badges.ts

// Make sure you have json-summary as a coverage reporter in your jest config.
// coverageReporters: ['json-summary', 'text', 'lcov']

import { readFileSync, mkdirSync, writeFileSync } from 'fs'
import { join } from 'path'
import { get } from 'https'
import { ok } from 'assert'

Promise.resolve().then(async () => {
	const outputDir = join(process.cwd(), 'badges')

	const summaryPath = join(process.cwd(), 'coverage', 'coverage-summary.json')
	const summary = JSON.parse(readFileSync(summaryPath, 'utf8')) as Summary
	const summaryKeys = ['lines', 'statements', 'functions', 'branches'] as const

	for (const summaryKey of summaryKeys) {
		const badgeURL = getBadgeURL(summary, summaryKey)
		const badgeFile = await download(badgeURL)
		const badgePath = join(outputDir, `coverage-${summaryKey}.svg`)

		mkdirSync(outputDir, { recursive: true })
		writeFileSync(badgePath, badgeFile, 'utf8')
	}
})

function getBadgeURL(summary: Summary, key: keyof jest.CoverageSummary) {
	const { pct } = summary.total[key]
	ok(typeof pct === 'number', `Something wrong with the ${key} coverage`)

	// https://shields.io/category/coverage
	const coverage = `${pct}${encodeURI('%')}`
	const colour = pct! < 80 ? 'red' : pct! < 90 ? 'yellow' : 'brightgreen'
	const url = `https://img.shields.io/badge/${key}-${coverage}-${colour}?logo=jest`

	return url
}

async function download(url: string) {
	return new Promise<string>((resolve, reject) => {
		get(url, (res) => {
			let file = ''
			res.on('data', (chunk) => (file += chunk))
			res.on('end', () => resolve(file))
		}).on('error', reject)
	})
}

type Summary = {
	total: jest.CoverageSummary
	[file: string]: jest.CoverageSummary
}

this is cool! thank you