Filtering object properties based on value

Here are two vanilla javascript options:

A.: Iterate over the object's keys and delete those having a falsey value.

var obj = {
  propA: true,
  propB: true,
  propC: false,
  propD: true,
};

Object.keys(obj).forEach(key => {
  if (!obj[key]) delete obj[key];
});

console.log(obj);

_{See Object.keys() and Array.prototype.forEach()}

B.: Iterate over the object's keys and add truthy values to a new object.

var obj = {
  propA: true,
  propB: true,
  propC: false,
  propD: true,
};

var filteredObj = Object.keys(obj).reduce((p, c) => {    
  if (obj[c]) p[c] = obj[c];
  return p;
}, {});

console.log(filteredObj);

_{See Object.keys() and Array.prototype.reduce()}

Lodash 4.0

Lodash 4.0 has _.pick, which takes an array of properties, and _.pickBy which takes a function as an argument and returns an object only containing the keys for which that function returns truthy which is what we want here, so it'd be:

filtered = _.pickBy(obj, function(value, key) {return value;})

Or, since _.pickBy defaults to using _.identity as it's second argument, (and that's essentially what we've written above,) it can just be written as:

filtered = _.pickBy(obj);

Underscore or Lodash prior to version 4.0

In underscore and old versions of lodash, there's just a single _.pick, which has both behaviors of _.pick and _.pickWith from v4. So you can do:

filtered = _.pick(obj, function(value, key) {return value;})

Or more succinctly:

filtered = _.pick(obj, _.identity)