Advent of Code 2019 day 8 solution (both parts)

methods.js

const {read} = require("../util/read")

class SpaceImage {
	constructor(width, height) {
		this.width = width
		this.height = height
		this.layers = []
	}

	importPixels(pixels) {
		const pixelsPerLayer = this.width * this.height
		const layerCount = pixels.length / pixelsPerLayer
		this.layers = Array(layerCount).fill(undefined).map((_, i) => pixels.slice(pixelsPerLayer*i, pixelsPerLayer*(i+1)))
		return this
	}

	checksum() {
		let layer = this.layers.sort((a, b) => (a.reduce((a, c) => a + (c === 0), 0) - b.reduce((a, c) => a + (c === 0), 0)))[0]
		console.log(layer)
		return layer.reduce((a, c) => a + (c === 1), 0) * layer.reduce((a, c) => a + (c === 2), 0)
	}

	renderVisible() {
		let rendered = null
		for (let i = this.layers.length-1; i >= 0; i--) {
			const layer = this.layers[i]
			if (rendered === null) {
				rendered = layer.slice()
			} else {
				for (let j = 0; j < layer.length; j++) {
					if (layer[j] !== 2) rendered[j] = layer[j]
				}
			}
		}
		return rendered
	}

	renderArt() {
		const rendered = this.renderVisible()
		let result = ""
		for (let y = 0; y < this.height; y++) {
			for (let x = 0; x < this.width; x++) {
				result += " .?"[rendered[x + this.width*y]]
			}
			result += "\n"
		}
		return result
	}
}

function loadImage(file) {
	const lines = read(file).asLines()
	const width = +lines[0]
	const height = +lines[1]
	const pixels = [...lines[2]].map(x => +x)
	return new SpaceImage(width, height).importPixels(pixels)
}

function checksumFile(file) {
	return loadImage(file).checksum()
}

function renderFile(file) {
	return loadImage(file).renderArt()
}

module.exports.checksumFile = checksumFile
module.exports.renderFile = renderFile