Poll function

poll.js

/**
 * Poll function
 * based on https://davidwalsh.name/essential-javascript-functions
 */
 
function poll(fn, callback, errback, timeout, interval) {
  var endTime = Number(new Date()) + (timeout || 2000);
  interval = interval || 100;
  
  (function p() {
    // If the condition is met, we're done! 
    if (fn()) {
      callback();
    } else if (Number(new Date()) < endTime) {
      setTimeout(p, interval);
    } else {
      errback(new Error('timed out for ' + fn + ': ' + arguments));
    }
  }());
}

// Use it like this ...

poll(
  function () {
    // Condition
    return that.value.length;
  },
  // Success
  function () {
    // ...
  },
  // Error
  function () {
    // ...
  },
  3000, // Poll timeout
  50 // Poll interval
);

promise-poll.js

export default function poll(
    fn,
    timeout,
    intervalArg,
    timeoutMessage,
) {
    const endTime = Number(new Date()) + (timeout || 2000);
    const interval = intervalArg || 100;

    const checkCondition = (resolve, reject) => {
        // If the condition is met, we're done!
        const 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(timeoutMessage));
        }
    };

    return new Promise(checkCondition);
}

///// Use like this:

poll(
  () => !window.ethereum.selectedAddress, // Condition
  10000, // Timeout
  100, // Poll interval
  'No ETH address available', // Timeout error
).then(callback);