// The polling function
function poll(fn, timeout, interval) {
var endTime = Number(new Date()) + (timeout || 2000);
interval = interval || 100;
var checkCondition = function(resolve, reject) {
// If the condition is met, we're done!
var result = fn();
if(result) {
resolve(result);
}
// If the condition isn't met but the timeout hasn't elapsed, go again
else if (Number(new Date()) < endTime) {
setTimeout(checkCondition, interval, resolve, reject);
}
// Didn't match and too much time, reject!
else {
reject(new Error('timed out for ' + fn + ': ' + arguments));
}
};
return new Promise(checkCondition);
}
// Usage: ensure element is visible
poll(function() {
return document.getElementById('lightbox').offsetWidth > 0;
}, 2000, 150).then(function() {
// Polling done, now do something else!
}).catch(function() {
// Polling timed out, handle the error!
});