underscore-updates.js

/**
 * This file extends Meteor's Underscore with selected methods from the latest version of Underscore,
 * copied from its source.
 */

// Internal function that returns an efficient (for current engines) version
// of the passed-in callback, to be repeatedly applied in other Underscore
// functions.
var optimizeCb = function(func, context, argCount) {
  if (context === void 0) return func;
  switch (argCount == null ? 3 : argCount) {
    case 1: return function(value) {
      return func.call(context, value);
    };
    case 2: return function(value, other) {
      return func.call(context, value, other);
    };
    case 3: return function(value, index, collection) {
      return func.call(context, value, index, collection);
    };
    case 4: return function(accumulator, value, index, collection) {
      return func.call(context, accumulator, value, index, collection);
    };
  }
  return function() {
    return func.apply(context, arguments);
  };
};

// A mostly-internal function to generate callbacks that can be applied
// to each element in a collection, returning the desired result — either
// identity, an arbitrary callback, a property matcher, or a property accessor.
var cb = function(value, context, argCount) {
  if (value == null) return _.identity;
  if (_.isFunction(value)) return optimizeCb(value, context, argCount);
  if (_.isObject(value)) return _.matcher(value);
  return _.property(value);
};

var property = function(key) {
  return function(obj) {
    return obj == null ? void 0 : obj[key];
  };
};

var getLength = property('length');

// Generator function to create the findIndex and findLastIndex functions
var createPredicateIndexFinder = function(dir) {
  return function(array, predicate, context) {
    predicate = cb(predicate, context);
    var length = getLength(array);
    var index = dir > 0 ? 0 : length - 1;
    for (; index >= 0 && index < length; index += dir) {
      if (predicate(array[index], index, array)) return index;
    }
    return -1;
  };
};

_.mixin({
  // Returns the first index on an array-like that passes a predicate test
  findIndex: createPredicateIndexFinder(1),
  findLastIndex: createPredicateIndexFinder(-1),

  // Returns the results of applying the iteratee to each element of the object
  // In contrast to _.map it returns an object
  mapObject: function(obj, iteratee, context) {
    iteratee = cb(iteratee, context);
    var keys = _.keys(obj),
    length = keys.length,
    results = {};
    for (var index = 0; index < length; index++) {
      var currentKey = keys[index];
      results[currentKey] = iteratee(obj[currentKey], currentKey, obj);
    }
    return results;
  }
});