Cannot read property 'bind' of undefined, Backbone.js

Question

I have the following function with a number of bindings...

showDialog: function(data) {
  var dialog = new dialog({
    onOk: function(text) {

      var obj = {
        data: text.data
      };

      this.model.save(obj, {
        method: 'PUT',
        success: function() {
          this.success().bind(this)
        }.bind(this)
      });
    }.bind(this)
  });
  Main.dialogArea.show(dialog);
}

Though the code works, it throws the following error in the console...

Uncaught TypeError: Cannot read property 'bind' of undefined

The error has to do with the following line this.success().bind(this).

I realized that this gets fixed if I use var self = this instead...

showDialog: function(data) {
  var self = this;
  var dialog = new dialog({
    onOk: function(text) {

      var obj = {
        data: text.data
      };

      self.model.save(obj, {
        method: 'PUT',
        success: function() {
          self.success()
        }
      });
    }
  });
  Main.dialogArea.show(dialog);
}

If I do this, the error disappears. Any idea as to why that is? Shouldn't both cases work the same? I am not using ES6 so I cannot use arrow functions, I would like to use bind().

T J · Accepted Answer · 2019-10-25 11:44:49Z

2

It should be

this.success.bind(this)

Instead of this.success().bind(this). Currently you're calling the function, function returns undefined and you're invoking .bind on it.

Side note:

Since you're doing

success: function() {}.bind(this)

You shouldn't have to bind a direct method invocation inside it, i.e

success: function() {
   this.success();
}.bind(this)

Should work, or just

success: this.success.bind(this)

edited Oct 25, 2019 at 11:44

answered Oct 25, 2019 at 8:19

T J

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