Pangram using Javascript

'use strict';

const fs = require('fs');

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', function(inputStdin) {
    inputString += inputStdin;
});

process.stdin.on('end', function() {
    inputString = inputString.split('\n');

    main();
});

function readLine() {
    return inputString[currentLine++];
}


/*
 * Complete the 'isPangram' function below.
 *
 * The function is expected to return a STRING.
 * The function accepts STRING_ARRAY pangram as parameter.
 */

function isPangram(pangram) {
    let alphabet = '';
    let assemble = '';
    let remove;
    let stringToCheck;
    let final;

    for(var k = 0; k < pangram.length; k++) {

        alphabet = "abcdefghijklmnopqrstuvwxyz";

        stringToCheck = pangram[k];

        for (var i = 0; i < stringToCheck.length; i++) {
            remove = alphabet.indexOf(stringToCheck[i]);

            if(stringToCheck[i] == alphabet[remove]) {
                alphabet = alphabet.replace(stringToCheck[i], '');
            }
        }
        console.log("Alphabet looks like: "+alphabet);
        if(alphabet.length == 0) {
            assemble = assemble.concat('1');
        }
        else {
            assemble = assemble.concat('0');
        }
        final = assemble;
    }
    return final;
}
function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

    const pangramCount = parseInt(readLine().trim(), 10);

    let pangram = [];

    for (let i = 0; i < pangramCount; i++) {
        const pangramItem = readLine();
        pangram.push(pangramItem);
    }

    const result = isPangram(pangram);

    ws.write(result + '\n');

    ws.end();
}