CODEWITHSUNDEEP
javascriptlodash
Gill Bates
Gill Bates

Reputation: 15157

Strange LoDash behavior

With this code:

var objects = [{'a': 1}, {'b': 2}];
var result1, result2;  

result1 = _(objects)
  .filter(_.partialRight(_.has, 'a'))
  .value();

result2 = _(objects)
  .filter(function(o){ return _.partialRight(_.has, 'a')(o);})
  .value();

result1 will be an empty array and result2 will be [{'a': 1}]. Why?

ps
Plunker:
http://plnkr.co/edit/6nhLBtq2id0GSYXVjhcX?p=preview

Upvotes: 1

Views: 109

Answers (2)

zerkms
zerkms

Reputation: 254926

This answer is an addition to the @elclanrs' one:

That's how you could do what you want without creating an anonymous function:

result1 = _(objects)
  .filter(_.compose(_.partialRight(_.has, 'a'), _.identity))
  .value();

Explanation:

The _.compose() function accepts the number of function references and applies them one by another, passing the result of execution from previous function to the next. And the _.identity() function returns the first passed argument.

So if we unwrap the _.compose(_.partialRight(_.has, 'a'), _.identity) expression it will look like:

function (a, b, c) {
    return _.partialRight(_.has, 'a')(_.identity(a, b, c));
}

Online demo: http://plnkr.co/edit/kU3MkrfSJol9c9JbGBqo?p=preview

References:

Upvotes: 0

elclanrs
elclanrs

Reputation: 94101

What's happening is that filter takes more arguments, that are being implicitly applied in composition, but not in application:

// what it looks like
.filter(_.partialRight(_.has, 'a'))

// what's happening
.filter(function(o,i,xs){return _.partialRight(_.has,'a')(o,i,xs);})

See here http://plnkr.co/edit/Q2Gz5vllUufzRvUuhqDQ?p=preview

Upvotes: 2

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