CODEWITHSUNDEEP
javascriptunderscore.jsthis
phizzy
phizzy

Reputation: 956

Javascript underscore.js- do I have to use a context parameter and 'this'?

In a tutorial I'm watching on underscore this code is used to demonstrate _.each:

var people = {
    names: ['Craig', 'John', 'Dan', 'Elijah'],
    getMessage: function(name) {
      return 'Hello there, ' + name + '!';
    }
};

_.each(people.names, function(element, index, list) {
  console.log(this.getMessage(element))
}, people);

It's explained that people gets passed as the context for the _.each call to bind this to the people object but I don't understand why this is necessary. In the body of the iterator function couldn't I just explicitly write out people.getMessage ?

like:

_.each(people.names, function(element, index, list) {
  console.log(people.getMessage(element));
});

Why use this and have to pass in a context at all?

Upvotes: 1

Views: 59

Answers (1)

Mark Polak
Mark Polak

Reputation: 403

Like mentioned in the comments, it is not necessary but it can be useful in certain cases. It also keeps the iterator function unaware of the scope above. It only knows it's dealing with objects that have a getMessage() method and not linked to a specific variable in the closure.

One example i can think of is to be able to reuse that for different objects that have the same sort of structure but are not named people in the scope.

var people = {
    names: ['Craig', 'John', 'Dan', 'Elijah'],
    getMessage: function(name) {
      return 'Hello there, ' + name + '!';
    }
};

var dogs = {
  names: ['Jimmy', 'Rufus', 'Woofie', 'Silly'],
  getMessage: function(name) {
      return 'Woof there, ' + name + '!';
    }
};

function logTheMessage(element) {
  console.log(this.getMessage(element));
}

_.each(people.names, logTheMessage, people);
_.each(people.names, logTheMessage, dogs);

Upvotes: 1

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