index.js

var _ = {};

/*********IDENTITY**********/
_.identity = function (val) {
  return val;
};

/*********FIRST**********/
_.first = function (array, n) {
  if (n) {
    for (let i = 0; i < n; i++) {
      return array[i];
    }
  } else {
    return array[0];
  }
};

/*********LAST**********/
_.last = function (array, n) {
  if (n) {
    for (let i = array.length - 1; i > array.length - (n + 1); i--) {
      return array[i];
    }
  } else {
    return array[array.length - 1];
  }
};

/*********EACH**********/
_.each = function (list, iteratee, context) {
  if (context) {
    iteratee.bind(context);
  }

  if (Array.isArray(list)) {
    for (let i = 0; i < list.length; i++) {
      iteratee(list[i], i, list);
    }
  } else if (typeof list === "object" && !Array.isArray(list)) {
    for (const [key, value] of Object.entries(list)) {
      iteratee(value, key, list);
    }
  }

  return list;
};

/*********INDEXOF**********/
_.indexOf = function (array, target, isSorted) {
  function binarySearch(arr, tar) {
    let low = 0;
    let high = array.length - 1;
    let mid;
    while (high >= low) {
      mid = Math.floor((low + high) / 2);

      if (arr[mid] == tar) {
        return mid;
      } else if (arr[mid] > tar) {
        high = mid - 1;
      } else {
        low = mid + 1;
      }
    }

    return -1;
  }

  if (isSorted && typeof isSorted === "boolean" && isSorted === "true") {
    binarySearch(array, target);
  } else if (isSorted && typeof isSorted === "number") {
    for (let i = isSorted; i < array.length; i++) {
      if (array[i] === target) {
        return i;
      }
    }
    return -1;
  } else {
    for (let i = 0; i < array.length; i++) {
      if (array[i] === target) {
        return i;
      }
    }
    return -1;
  }
};

/*********FILTER**********/
_.filter = function (collection, test, context) {
  if (context) {
    test.bind(context);
  }

  let resultArr = [];
  for (let i = 0; i < collection.length; i++) {
    if (test(collection[i])) {
      resultArr.push(collection[i]);
    }
  }

  return resultArr;
  // "predicate is transformed through iteratee to facilitate shorthand syntaxes."
  // WTF DOES THAT MEAN AVI????
};

/*********REJECT**********/
_.reject = function (collection, test) {};

/*********UNIQ**********/
_.uniq = function (array) {};

/*********MAP**********/
_.map = function (collection, iterator) {};

/*********PLUCK**********/
_.pluck = function (collection, key) {};

/*********INVOKE*********/
_.invoke = function (collection, func, args) {};

/*********REDUCE**********/
_.reduce = function (collection, iterator, accum) {};

/*********CONTAINS*********/
_.contains = function (collection, target) {};

/*********EVERY**********/
_.every = function (collection, iterator) {};

/********SOME**********/
_.some = function (collection, iterator) {};

/*********EXTEND**********/
_.extend = function (obj) {};

/*********DEFAULTS**********/
_.defaults = function (obj) {};

/*********ONCE**********/
_.once = function (func) {};

/*********MEMOIZE*************/
_.memoize = function (func) {};

/*********DELAY*********/
_.delay = function (func, wait) {};

/*********SHUFFLE**********/
_.shuffle = function (array) {};

/*********SORTBY**********/
_.sortBy = function (collection, iterator) {};

/*********ALTERNATE SORTBY USING MANUAL SORT**********/
_.sortByManual = function (collection, iterator) {};

/*********ZIP**********/
_.zip = function () {};

/*********FLATTEN**********/
_.flatten = function (nestedArray) {};

/*********UNION**********/
_.union = function () {};

/*********INTERSECTION**********/
_.intersection = function () {};

/*********DIFFERENCE**********/
_.difference = function (array) {};