acceptance.js

    client.addCommand("waitForFunc", function(checker, timeout) {
        if (typeof timeout === 'function') {
            cb = timeout
            timeout = this.options.waitforTimeout
        }
        return new Promise(function(fulfill, reject) {
            var start = new Date().getMilliseconds()
            var timer = setTimeout(function run() {
                if (!checker()) {
                    if (new Date().getMilliseconds() > start + timeout) {
                        reject('timeout')
                    }
                    timer = setTimeout(run, 100)
                } else {
                    fulfill(null)
                }
            }, 100)
        })
    });