backdoorthen/index.js

Cheat codes for promises

/**
 * Assess the value of an input variable to determine whether
 * a given thenable should be called or bypassed in favor of returning mocked data instead
 * @param {Object} params
 * @param {*} params.input The value the outcome depends upon (String expected by default assessor)
 * @param {*} params.resolvedValue The data the mocked promise should resolve with
 * @param {*} params.rejectedValue The data the mocked promise should reject with
 * @param {Object} params.config Default behaviour overrides
 * @param {Number} params.config.fast The short delay before the mocked promise settles
 * @param {Number} params.config.slow The long delay before the mocked promise settles
 * @param {String} params.config.separator The character separating each keyword backdoor looks for
 * @param {Function} params.config.assessor Mean to override backdoor's logic entirely
 * @param {Boolean} params.config.enabledInProd False by default, non-boolean values equate to false
 * @returns {Function} A function that takes in the thenable that should be either called or bypassed
 */
function backdoor(params) {
  return function(thenable) {
    var fast = 1000;
    var slow = 5000;
    var separator = '-';
    var enabledInProd = false;
    var assess = assessor;
    if (params.config) {
      if (params.config.fast || params.config.fast === 0) { fast = params.config.fast; }
      if (params.config.slow || params.config.slow === 0) { slow = params.config.slow; }
      if (params.config.separator) { separator = params.config.separator; }
      if (params.config.assessor) { assess = params.config.assessor; }
      if (params.config.enabledInProd === true) { enabledInProd = true; }
    }
    if (process.env.NODE_ENV !== 'production' || enabledInProd) {
      var decision = assess(params.input, separator);
      if (decision.isBackdoor) {
        var delay = decision.isFast ? fast : slow;
        return function() {
          return new Promise(function(resolve, reject) {
            return setTimeout(function() {
              return decision.doResolve
                ? resolve(params.resolvedValue)
                : reject(params.rejectedValue);
            }, delay);
          });
        };
      }
    }
    return thenable;
  }
}

function assessor(input, separator) {
  var backdoorChunks = input.toLowerCase().split(separator);
  return {
    isBackdoor: backdoorChunks[0] === 'backdoor',
    doResolve: backdoorChunks[1] === undefined || backdoorChunks[1] === 'fast',
    isFast: backdoorChunks[1] === 'fast' || backdoorChunks[2] === 'fast'
  };
}

module.exports = backdoor;