wait.js

function wait(duration) {
    // Create and return a new Promise
    return new Promise((resolve, reject) => { // These control the Promise
        // If the argument is invalid, reject the Promise
        if (duration < 0) {
            reject(new Error("Time travel not yet implemented"));
        }
        // Otherwise, wait asynchronously and then resolve the Promise.
        // setTimeout will invoke resolve() with no arguments, which means
        // that the Promise will fulfill with the undefined value.
        setTimeout(resolve, duration);
    });
}