Wait for a jQuery selector in the browser using promises

jsPromises.js

/**
 * This is too show the use of waiting for a jquery selector in the browser
 * using promises. Much like how webdriverio works from outside the browser.
 * 
 * Tested with jQuery v1.11.3 and chrome Version 48.0.* (64-bit)
 **/


/**
 * Wait for a jquery css selector
 * @param  {String} selector  - Css selector String
 * @param  {Integer} timeout  - max time ot wait in milliseconds
 * @return {Array}            - Jquery selections
 */
function waitForExists(selector, timeout, interval) {
    // init
    if (interval===undefined) interval=250;
    if (timeout===undefined)  timeout=15000;
    var start = Date.now();

    /** check is exists, or for timeout, or call itself **/
    function checkExists(resolve, reject) {
        if (selector && $(selector).length) {
            console.debug('Succeeded in ', (Date.now() - start),', checkExists:',selector);
            return resolve($(selector));
        } else if (timeout && (Date.now() - start) >= timeout)
            return reject(new Error('Timed out in '+timeout+', checkExists:'+selector));
        else
            return setTimeout(checkExists.bind(this, resolve, reject), interval);
    }

    return new Promise(checkExists);
}

function waitForNotExists(selector, timeout, interval) {
    // init
    if (interval===undefined) interval=250;
    if (timeout===undefined)  timeout=15000;
    var start = Date.now();

    /** check is not exists, or for timeout, or call itself **/
    function checkNotExists(resolve, reject) {
        if (selector && !$(selector).length) {
            console.debug('Succeeded in ', (Date.now() - start),', checkNotExists:',selector);
            return resolve($(selector));
        } else if (timeout && (Date.now() - start) >= timeout)
            return reject(new Error('Timed out in '+timeout+', checkNotExists:'+selector));
        else
            return setTimeout(checkNotExists.bind(this, resolve, reject), interval);
    }

    return new Promise(checkNotExists);
}

/** Utility to click a selector when it exists **/
function clickWhenExists(selector, timeout, interval) {
    return waitForExists(selector, timeout, interval)
        .then($dom => {
            return $dom.click();
        });
}

/** Utility to click a selector if it exists **/
function clickIfExists(selector, reject) {
    var $dom = $(selector);
    if ($dom.length){
        console.debug('clickIfExists '+'found selector '+selector);
        return $dom.click();
    } else {
        console.debug('clickIfExists '+'did not find selector '+selector);
        return reject ? reject($dom): false;
    }
}