How can you implement a `filter()` method for JavaScript objects?

JavaScript: Implementing filter() for Objects

JavaScript provides the filter() prototype for Array types, but this functionality is absent for Object types. To address this limitation, let's explore how to create a filter() implementation specifically for objects.

Implementation:

Object.prototype.filter = function(predicate) {
  var result = {};

  for (key in this) {
    if (this.hasOwnProperty(key) && !predicate(this[key])) {
      result[key] = this[key];
    }
  }

  return result;
};

While this implementation works in isolation, adding it to a site using jQuery 1.5 and jQuery UI 1.8.9 may trigger JavaScript errors.

Alternative Solutions:

Instead of modifying the Object prototype, consider these standalone or utility functions:

1. Using reduce and Object.keys:

Object.filter = (obj, predicate) => 
  Object.keys(obj)
        .filter(key => predicate(obj[key]))
        .reduce((res, key) => (res[key] = obj[key], res), {});

2. Using map and spread syntax:

Object.filter = (obj, predicate) => 
  Object.entries(obj)
        .filter(([key, value]) => predicate(value))
        .reduce((acc, [key, value]) => ({ ...acc, [key]: value }), {});

3. Using Object.entries and Object.fromEntries:

Object.filter = (obj, predicate) => 
  Object.fromEntries(
    Object.entries(obj).filter(([key, value]) => predicate(value))
  );

Example Usage:

var scores = {
  John: 2,
  Sarah: 3,
  Janet: 1
};
var filtered = Object.filter(scores, score => score > 1); 
console.log(filtered);

These alternative solutions provide a cleaner and more maintainable way to filter object properties while preserving the original object.

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