lowbar.js

/*

DONE --------------------
1. identity
2. first
3. last
4. each
5. indexOf  (can't get binary search to work faster)
6. filter
7. reject
8. uniq
9. map
10. pluck
11. reduce
12. contains
13. every
14. some
Additional: where
15. extend
16. defaults
17. once
18. memoize
* 19. delay // not sure how to test this, not sure if setTimeout is working too
20. shuffle
21. invoke
22. sortBy
23. zip
24. flatten
25. intersection

26. difference

TO DO -----------------
27. throttle

*/

var _ = {};

_.identity = function (value) {
  return value;
};

_.first = function (arr, num) {
  if (!arr) return undefined;
  return !num ? arr[0] : arr.slice(0, num);
};

_.last = function (arr, num) {
  if (!arr) return undefined;
  var len = arr.length;
  return !num ? arr[len - 1] : arr.slice(len - num);
};

_.each = function (list, iteratee, context) {
  iteratee = iteratee || _.identity;
  context = context || this;
  // handle arrays
  if (Array.isArray(list)) {
    for (var i = 0; i < list.length; i++) {
      iteratee.call(context, list[i], i, list);
    }
  } else if (typeof list === 'object') { // handle objects
    for (var key in list) {
      iteratee.call(context, list[key], key, list);
    }
  }
  return list;
};

_.indexOf = function (list, value, isSorted) {
  if (!list || !value) return -1;

  // use binary search for when isSorted is TRUE
  if (isSorted === true) {
    var offset = null;
    while (list.length > 1) { // slice in two - take second half
      var secondHalf = list.slice(Math.floor(list.length / 2));
      if (secondHalf[0] <= value) { // keep second half
        offset += Math.floor(list.length / 2);
        list = secondHalf;
      } else { // retain the first half
        list = list.slice(0, Math.floor(list.length / 2));
      }
    }
    return offset;
  }

  // perform standard search for when isSorted is not TRUE
  var startIndex;
  typeof isSorted === 'number' ? startIndex = isSorted + 1 : startIndex = 0;
  for (var i = startIndex; i < list.length; i++) {
    if (list[i] === value) return i - startIndex;
  }
  return -1;
};

_.filter = function (list, predicate, context) {
  list = list || [];
  predicate = predicate || _.identity;

  var filteredArray = [];
  for (var i = 0; i < list.length; i++) {
    if (predicate.call(context, list[i])) {
      filteredArray.push(list[i]);
    }
  }
  return filteredArray;
};

_.reject = function (list, predicate, context) {
  list = list || [];
  predicate = predicate || _.identity;

  var filteredArray = [];
  for (var i = 0; i < list.length; i++) {
    if (!predicate.call(context, list[i])) {
      filteredArray.push(list[i]);
    }
  }
  return filteredArray;
};

_.uniq = function (list, isSorted, iteratee) {
  list = list || [];
  isSorted = isSorted || false;
  iteratee = iteratee || _.identity;

  var uniqueArray = [];
  for (var i = 0; i < list.length; i++) {
    if (isSorted && (list[i] === list[i - 1])) {
      continue; // skip this iteration if this element is same as previous element
    }
    if (uniqueArray.indexOf(list[i]) === -1) {
      uniqueArray.push(list[i]);
    }
  }
  return uniqueArray;
};

_.map = function (list, iteratee, context) {
  list = list || [];
  iteratee = iteratee || _.identity;
  context = context || this;

  var result = [];
  if (Array.isArray(list)) {
    for (var i = 0; i < list.length; i++) {
      result.push(iteratee.call(context, list[i], i, list));
    }
  } else if (typeof (list) === 'object') {
    for (var key in list) {
      result.push(iteratee.call(context, list[key], key, list));
    }
  }
  return result;
};

_.pluck = function (list, propertyName) {
  return _.map(list, function (obj) {
    return obj[propertyName];
  });
};

_.reduce = function (list, iteratee, memo, context) {
  var copyList = list;

  if (memo === undefined) {
    // make a copy of the list which we can modify
    copyList = list.slice();
    memo = copyList.shift();
  }
  for (var i = 0; i < copyList.length; i++) {
    memo = iteratee.call(context, memo, copyList[i], i, copyList);
  }
  return memo;
};

_.contains = function (list, value, fromIndex) {
  fromIndex = fromIndex || 0;
  return _.indexOf(list.slice(fromIndex), value) !== -1;
};

_.every = function (list, predicate, context) {
  list = list || [];
  predicate = predicate || _.identity;
  for (var i = 0; i < list.length; i++) {
    if (!predicate.call(context, list[i])) return false;
  }
  return true;
};

_.some = function (list, predicate, context) {
  list = list || [];
  predicate = predicate || _.identity;
  for (var i = 0; i < list.length; i++) {
    if (predicate.call(context, list[i])) return true;
  }
  return false;
};

_.where = function (list, properties) {
  properties = properties || {};
  var result = [];
  _.each(list, function (obj) {
    var match = true;
    for (var key in properties) {
      if (properties[key] !== obj[key]) {
        match = false;
        break;
      }
    }
    if (match) result.push(obj);
  });
  return result;
};

_.extend = function (destination, ...sources) {
  sources = [...arguments];
  sources.shift();
  _.each(sources, function (sourceObj) {
    destination = Object.assign(destination, sourceObj);
  });
  return destination;
};

_.defaults = function (object, ...defaults) {
  _.each(defaults, function (defaultObj) {
    _.each(defaultObj, function (value, key) {
      if (object[key] === undefined) object[key] = value;
    });
  });
  return object;
};

_.once = function (myFunction) {
  var hasRun = false;
  var result;
  return function () {
    if (!hasRun) {
      hasRun = true;
      result = myFunction.apply(null, arguments);
    }
    return result;
  };
};

_.memoize = function (myFunction, hashFunction) {
  var cache = {};
  var result;

  var speedyFunction = function () {
    var stringyArgs;
    if (hashFunction) {
      var args = [].slice.call(arguments);
      stringyArgs = hashFunction.apply(null, args);
    } else {
      stringyArgs = JSON.stringify(arguments[0]);
    }
    if (cache.hasOwnProperty(stringyArgs)) {
      result = cache[stringyArgs];
    } else {
      result = myFunction.apply(null, arguments);
      cache[stringyArgs] = result;
    }
    return result;
  };

  // save the cache as a property on the function
  speedyFunction.cache = cache;
  return speedyFunction;
};

_.delay = function (myFunc, delay, ...args) {
  return setTimeout(function () {
    myFunc.apply(null, args);
  }, delay);
};

_.shuffle = function (arr) {
  var list = arr.slice();
  var shuffledList = [];
  var index;
  while (list.length > 0) {
    index = Math.floor(Math.random() * list.length);
    shuffledList.push(list[index]);
    list.splice(index, 1);
  }
  return shuffledList;
};

_.invoke = function (list, method, ...args) {
  return _.map(list, function (element) {
    return element[method](...args);
  });
};

_.sortBy = function (list, iteratee, context) {
  list = list || [];
  iteratee = iteratee || _.identity;
  if (typeof iteratee === 'function') {
    list = _.map(list, function (element) {
      return {
        original: element,
        modified: iteratee.call(context, element)
      };
    });
    // sort my modified value, but return original value
    list.sort(function (a, b) {
      return (a.modified < b.modified) ? -1 : (a.modified > b.modified) ? 1 : 0;
    });
    // return only the original values, in new order
    return _.pluck(list, 'original');
  } else if (typeof iteratee === 'string') {
    return list.sort(function (a, b) {
      return (a[iteratee] < b[iteratee]) ? -1 : (a[iteratee] > b[iteratee]) ? 1 : 0;
    });
  }
};

_.zip = function (...arrays) {
  var maxLength = _.reduce(arrays, function (acc, element) {
    return element.length > acc ? element.length : acc;
  }, 0);
  var result = [];
  for (var i = 0; i < maxLength; i++) {
    var newArr = [];
    _.each(arrays, function (singleArr) {
      newArr.push(singleArr[i]);
    });
    result.push(newArr);
  }
  return result;
};

_.flatten = function (list, shallow) {
  var result = [];
  var flattenedOneLevel = false;

  function flatten (list) {
    _.each(list, function (element) {
      if (!Array.isArray(element)) { // NOT ARRAY
        result.push(element);
      } else { // ARRAY
        if (flattenedOneLevel && shallow) {
          result.push(element);
        } else {
          flattenedOneLevel = true;
          flatten(element);
        }
      }
    });
    flattenedOneLevel = false;
  }

  flatten(list);
  return result;
};

_.intersection = function (...arrays) {
  var result = [];
  _.each(arrays[0], function (element) {
    var foundInEvery = _.every(arrays, function (array) {
      return _.contains(array, element);
    });
    if (foundInEvery) result.push(element);
  });
  return result;
};

_.difference = function (array, ...others) {
  var result = [];
  _.each(array, function (element) {
    var notInOthers = _.every(others, function (array) {
      return !_.contains(array, element);
    });
    if (notInOthers) result.push(element);
  });
  return result;
};

if (typeof module !== 'undefined') {
  module.exports = _;
}