使用_.filter重新创建Underscore.js _.reject

Question

I am working on a project where I am re-creating many of the fundamental functions included in Underscore.js. I have successfully written the _.filter() function, using my implementation of _.each() (both are below).

Additionally, I have been able to write the _.reject() function using the "easy" way out (simply copy/pasting the _.filter() code and adding the ! in the appropriate place), but for the learning experience, I am looking to develop an alternate implementation that uses actually calls _.filter().

I've seen questions and responses that show how to do this using another Underscore function, _.negate(), but I haven't implemented this function yet in the project, so my question is, is there a way to create _.reject() using a call to the _.filter() function WITHOUT using _.negate()?

_.filter:

_.filter = function(collection, test) {
  var results = [];

  _.each(collection, function(itemTested) {
    if (test(itemTested)) {
      results.push(itemTested);
    }
  });

  return results;
};

_.each:

_.each = function(collection, iterator) {
  if(Array.isArray(collection)) {
    for(var i = 0; i < collection.length; i++) {
      iterator(collection[i], i, collection);
    }
  }

  else {
    for(var property in collection) {
      iterator(collection[property], property, collection);
    }
  }
};

Current version of _.reject:

_.reject = function(collection, test) {
  var results = [];

  _.each(collection, function(itemTested) {
    if (!test(itemTested)) {
      results.push(itemTested);
    }
  });

  return results;
};

Answer 1

Reject function using filter:

var _ = {};

_.reject = function(col, fn) {
  return col.filter(function(v) {
    return !fn(v);
  });
}

// or using your _.filter function
_.reject = function(col, fn) {
  return _.filter(col, function(v) {
    return !fn(v);
  });
}

var odd = _.reject([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });

console.log(odd); // [1,3,5]

JS Bin Example

http://jsbin.com/juyos/1/edit

Answer 2

Well, even if you're not calling _.negate , you still gives you an idea what it would do:

_.reject = function(collection, test) {
  return _.filter(collection, function(el, i, collection) {
    return !test(el, i, collection);
  });
};