bind() on promise error function - javascript

Question

I found this codesnippet. Can somebody explain the purpose of the .bind(this) in this context? Where would we be able to access this now? In the resolved promise?

get: function(endpoint, params, callback) {
  var cb = callback || angular.noop;
  var deferred = $q.defer();

  $http.get(
    endpoint,
    params
  ).
  success(function(data) {
    deferred.resolve(data);
    return cb();
  }).
  error(function(err) {
    deferred.reject(err);
    return cb(err);
  }.bind(this));

  return deferred.promise;
}

Dmitri Pavlutin · Accepted Answer · 2016-05-23 05:45:36Z

1

The purpose of the bind(newContext) method of the function object is to return a new function with the context this as the first parameter passed to bind().

For example:

var message = {text: 'I am the context'};

function tryMe() {
  console.log(this);
}

tryMe(); // will print undefined (in strict mode) or global object
tryMe.bind(message)(); // will print '{text: 'I am the context'}'

In your example, the idea of using bind() is to keep the context this of the get() method in the error handler:

.error(function(err) {
    deferred.reject(err);
    //now use this.get() for example
    return cb(err);
  }.bind(this));

However no methods associate with the new context were called in the handler.

See more details in Gentle explanation of this.

edited May 23, 2016 at 5:45

answered Feb 26, 2016 at 18:34

Dmitri Pavlutin

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