1-numberguess.js

alert('Think of a number from 1 to 100...');
var currGuess = 50;

do {
    var response = prompt('I guess ' + currGuess + ' - am I too [h]igh, too [l]ow, or [r]ight on?');
    if (response[0].toLowerCase() === 'h') {
        currGuess--;
    } else if (response[0].toLowerCase() === 'l') {
        currGuess++;
    } else {
        break;
    }
} while (true);

alert('Got it! Your number is ' + currGuess);

2-numberguess.js

alert('Think of a number from 1 to 100...');
var currGuess = 50, max = 100, min = 0;

do {
    var response = prompt('I guess ' + currGuess + ' - am I too [h]igh, too [l]ow, or [r]ight on?');
    if (response[0].toLowerCase() === 'h') {
        max = currGuess;
    } else if (response[0].toLowerCase() === 'l') {
        min = currGuess;
    } else {
        break;
    }
    currGuess = Math.round(min + (max - min) / 2);
} while (true);

alert('Got it! Your number is ' + currGuess);