Reading two strings using readline

Question

I'm having a hard time undestanding how to use the readline library from NodeJS to read two different strings for a Kattis challenge.

See, in their documentation there's the following example:

const readline = require('readline');

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});

rl.on('line', (line) => {
    var nums = line.split(' ');
    var a = parseInt(nums[0]);
    var b = parseInt(nums[1]);
    /*Solve the test case and output the answer*/
});

I need to read two strings and then manipulate them. I've already tried doing:

const readline = require('readline');

var string1 = '';
var string2 = '';

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});

rl.on('line', (line) => {
    var string1 = line;
});

rl.on('line', (line) => {
    var string2 = line;
});

//manipulating strings...

and even:

const readline = require('readline');

var string1 = '';
var string2 = '';

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});

rl.question('', (answer) => {
    var string1 = answer;
});

rl.question('', (line) => {
    var string2 = answer;
});

//manipulating strings...

But I keep getting a Run time error. What am I doing wrong, exactly?