tutorial-terminal-step-4.js

// Returns a random number to simulate our thinking.
function getThinkingTime () {
    var base      = 500,
        deviation = 250;

    return (Math.random() * deviation * 2) + (base - deviation);
}

// Starts the animation.
function startAnimation () {
    interval = setInterval(function () {
        // Our copy of the line is empty.
        if (line.length === 0) {
            // Move the pointer to the next line.
            pointer = pointer + 1;

            // The pointer is inside the range, copy the new line.
            if (pointer !== strings.length) {
                line = strings[pointer];
                
                // Thinking before typing, always a good idea!
                pauseAnimation(getThinkingTime());
                return;
            }
            // The pointer is out of range, stop the animation,
            // reset the interval variable, and exit the loop.
            else {
                return interval = clearInterval(interval);
            }
        }

        // Print the first character from our copy of the line.
        app.print(line[0]);
        // Now delete the first character, so the second character
        // becomes the first, the third becomes second, etc.
        line = line.substr(1);

        // If we have reached the end of the line, fake the
        // Enter key press action.
        if (!line) {
            pauseAnimation(getThinkingTime(), function () {
                app.println();
            });
        }
    }, 80);
}

// Stop and start the animation after a while,
// creating an illusion of the pause.
function pauseAnimation (time, callback) {
    clearInterval(interval);
    setTimeout(function () {
        if (typeof callback === 'function') {
            callback();
        }
        startAnimation();
    }, time);
}

// Initialise the animation.
startAnimation();