index.js

#!/usr/bin/env node

process.stdin.resume();
process.stdin.setEncoding("utf8");
process.stdin.on("data", function(data){
    processInput(data);
});

let maskChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()-_=+{}[]:;|\"'<>,.?/".split("");

class Char {
    constructor(initial, animationInterval){
        this.initial = initial;
        this.decrypted = false;
        this.animationInterval = animationInterval;
        this.crypted = this.generateCrypted();
    }
    generateCrypted(){
        return Char.doNotModifyChars.includes(this.initial) ? this.initial : maskChars[Math.floor(Math.random()*maskChars.length)]
    }
    initDecrypt(){
        const gen = this.decrypt();
        return new Promise((resolve)=>{
            setInterval(()=>{
                const {done} = gen.next();
                if(done) {
                    resolve();
                }
            }, 300)
        });
    }
    getValue(){
        return this.decrypted ? this.initial : this.crypted;
    }
    * decrypt(){
        for(let i=0;i<this.animationInterval;i++){
            yield this.crypted = this.generateCrypted();
        }
        this.decrypted = true;
        yield this.initial;
    }
}
Char.doNotModifyChars = ["\n"," "];

class DataProcessor {
    constructor(){
        this.chars = null;//It supposed to contain all chars
        this.rows = [];//It has all rows with text
        this.decrypted = false;
    }
    getTextFromCryptedChars(chars){
        return [].concat.apply([], chars).reduce((res, char)=>{
            return res.push(char.getValue()), res;
        },[]).join("");
    }
    getCryptedCharsFromText(text){
        this.rows = text.split("\n");
        this.chars = this.rows.reduce((res, row)=>{//[new Char, new Char, new Char,new Char, new Char, new Char...]
            row = row.split("").map((char)=>{
                return new Char(char, (Math.random()*20|0));
            });
            row.unshift(new Char("\n"));
            return [...res, ...row];
        }, []);
        return this.chars;
    }
    getCryptedText(text){
        return this.getTextFromCryptedChars(this.getCryptedCharsFromText(text))
    }
    initDecrypt(){
        var pr = this.chars.map((char)=>{
            return char.initDecrypt();
        });
        Promise.all(pr).then(()=>{
            this.decrypted = true;
        })
    }
    getSnapshot(){
        let value = this.getTextFromCryptedChars(this.chars);
        return {
            done: this.decrypted,
            value
        }
    }
}


let processInput = (data) => {
    const dataProcessor = new DataProcessor();
    process.stdout.write(dataProcessor.getCryptedText(data));

    let interval = setInterval(()=>{
        const l = dataProcessor.rows.length;
        let {done, value} = dataProcessor.getSnapshot();

        process.stdout.write('\033['+l+'A');
        process.stdout.clearScreenDown();
        process.stdout.write(value);

        if(done){
            clearInterval(interval);
            process.exit();
        }

    }, 75);

    dataProcessor.initDecrypt();
};