Javascript file to encode images (png, jpg, jpeg) into WebP format

webp.js

const fs = require("fs")
const path = require('path')
const exec = require("child_process").exec
const prompt = require('prompt')

// quality factor (0:small..100:big), default=75
const WEBP_QUALITY_FACTOR = 80
const WEBP_EXT = '.webp'
const TO_WEBP_DEFAULT_FOLDER = 'src/assets/images'

const FIELD_CHOICE = ['to WebP(1) ; from WebP(2)']
const FIELD_FOLDER = [`folder (default: ${TO_WEBP_DEFAULT_FOLDER})`]


/**
 * Allows to encode image into WebP format
 * 
 * @param dir Folder to scan
 */
var imagesToWebps = function (dir) {
    fs.readdirSync(dir).forEach(function (file) {
        file = dir + '/' + file
        var stat = fs.statSync(file)
        if (stat && stat.isDirectory()) {
            imagesToWebps(file)
        } else {
            // Add another file image extension if needed
            if (file.endsWith('.jpg') || file.endsWith('.jpeg') || file.endsWith('.png')) {
                console.log(file)
                var filename = path.basename(file, path.extname(file))
                var pathname = path.dirname(file) + '/'
                // cwebp encoder command: https://developers.google.com/speed/webp/docs/cwebp
                var cmd = `cwebp -q ${WEBP_QUALITY_FACTOR} ${file} -o ${pathname}${filename}${WEBP_EXT}`
                // console.log('   ' + cmd);
                exec(cmd, (error, stdout, stderr) => {
                    if (error) {
                        console.log('   stderr:' + stderr)
                    } else {
                        fs.unlink(file, function () {
                            console.log(`   ${file} deleted`)
                        });
                    }
                });
            }
        }
    });
};

/**
 * Main and first function to start this program
 * 
 * @see https://developers.google.com/speed/webp/
 */
function start() {
    prompt.start()
    prompt.get(FIELD_CHOICE, function (err, promptValue) {
        if (err) {
            console.error(err)
        }
        switch (promptValue[FIELD_CHOICE[0]]) {
            case "1":
                prompt.get(FIELD_FOLDER, function (err, promptValue) {
                    if (err) console.error(err)
                    var value = promptValue[FIELD_FOLDER[0]]
                    if (value === "") {
                        value = TO_WEBP_DEFAULT_FOLDER
                    }
                    imagesToWebps(value);
                });
                break;
            case "2":
                console.warn('TODO: decoder')
                break;
        }
    });
}

start()