jsfc.js

/* 
 * groupBy
 * =======
 * Given array of objects iter, group by object property prop and return
 */
function gb(iter,prop) {
  var r = {};
  iter.map(function(e) {
    console.log(e);
    (r[e[prop]] = r[e[prop]] || []).push(e);
  });
  return r;
}

/* 
 * extend
 * ======
 * - Extend ("Assign") object non-inherited properties from arguments
 * - Bonus points for mentioning this is available as _.extend(), _.assign, or Object.assign() in ES6
 */
Object.prototype.e = function() {
  for (var i=0;i<arguments.length;i++) {
    for (var prop in arguments[i]) {
      if(arguments[i].hasOwnProperty(prop)) {
        this[prop] = arguments[i][prop];
      }
    }
  }
}

/*
 * counter
 * =======
 * - Increments and returns a counter on every call
 * - Bonus points for talking about closures or IIFE
 * - Synonyms: "add", "increment"
 */
var c = (function() { 
  var _c = 0;
  return function() { return _c ++ };
})();

/* 
 * find
 * ====
 * - Return first matching item in this array based on a predicate
 * - Bonus points for pointing out this is a (bad) polyfill for an ES6 method, and implemented in many other _ type libs
 */
Array.prototype.f = function(pred) {
  for (var i in this) {
    if (pred(this[i])) {
      return this[i];
    }
  }
}

/*
 * parseURL
 * ========
 * Given a url string u and an anchor property p - "host", or "pathname" for example - return the requested property
 */
function pu(u,p) { 
  var a = document.createElement('a');
  a.href = u;
  return a[p];
}

/*
 * toggleActive
 * ===========
 * - Toggle presence of class 'active' for all DOM elements with class x
 * - Assumes a little familiarity with jQuery and CSS selectors, which seems reasonable
 * - Bonus points for understanding the ~= (contains) syntax
 */
var ta = function(x) {
  $('[class~=' + x + ']').each(function() {
    $(this).toggleClass('active');
  });
};

/* 
 * disableClick
 * =============
 * - Disable click events on elements matching selector
 * - Again assumes jquery
 */
function dc(selector) {
  $(selector).click(function(e) {
    e.preventDefault();
    e.stopPropagation();
  });
}

/* 
 * cachePromise 
 * ============
 * - On success, memoise / "cache" the result of a potentially expensive promise, subsequently return it in preference to running the operation again
 * - Assumes knowlege of a promise library (angular/react/bluebird.js/Q etc, or ES6 promises)
 * - I've used ES6 style promises here becaue they should be simple enough to work out if you know any other promise implementation
 */
var c;
function cp() {
  return new Promise(function(resolve,reject) {
    if (c) {
      resolve(c);
    } else {
      callOut().then(function(success) {
        c = success;
        resolve(success);
      });
    }
  });
}
 
/* 
 * promisify
 * =========
 *  - Turn x into a pre-resolved promise
 *  - Again, uses ES6-ish syntax
 *  - Bonus points: variants of this already exist in bluebird.js, angular, etc with different names
 *  - Synonyms: "when", "$when", "toPromise", "resolve" , etc
 */
var p = function(x) {
  return new Promise(function(resolve,reject) {
    resolve(x);
  });
}

/* 
 * callbackToPromise
 * =================
 *  - Again I'm using ES6 syntax here because it's probably more ubiquitous
 *  - Return a promise with results of calling error,callback style function func.
 *  - Synonyms for p: 'promisify', 'toPromise', 'asPromise', 'callback to promise', etc. 
 */
function c2p(func) {
  return new Promise(function(resolve,reject) {
    func(function(error,result) {
      if (error) {
        reject(error);
      } else {
        resolve(result);
      }
    });
  });
}