Issues have arisen with the execution of JavaScript code inside a callback function

When the warnBeforeNew variable is set to false in the JavaScript code below, the file open function works as expected. However, when warnBeforeNew is true, an error occurs stating "Uncaught TypeError: Cannot read property 'root' of undefined".

I'm not sure if this issue is related to scoping, but I need help getting the file loading code to execute properly within the callback function. Thank you.

Editor.prototype.open = function(path) {
  if (Editor.warnBeforeNew == true){
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew = false;
          this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }
};

Answer №1

It is important to save the value of this because the callback function may have a different receiver compared to the main external function:

if (Editor.warnBeforeNew==true){
    var current = this; // Feel free to choose a more descriptive name...
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew=false;
          current.filesystem.root.getFile(path, {}, current.load.bind(current), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }

Answer №2

It is important to bind the submitCallback in your showDialog method as well, especially because it accesses this.filesystem.root..., which can lead to failures if not properly bound.

this.showDialog({
    ...,
    submitCallback: function() {
      Editor.warnBeforeNew = false;
      this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
    }.bind(this)
//    ^^^^^^^^^^
});

Answer №3

Ensure you capture the scope outside of the callback function and make use of it.

Editor.prototype.open = function(path) {
var that=this;
  if (Editor.warnBeforeNew==true){
    this.showDialog({
        dialogLabel: 'You have unsaved changes. Are you sure you want to discard them and open a different file?',
        submitLabel: 'Discard',
        cancelLabel: 'Cancel',
        submitCallback: function() {
          Editor.warnBeforeNew=false;
          that.filesystem.root.getFile(path, {}, that.load.bind(that), error.bind(null, "getFile " + path));
        }
    });
  } else {
    this.filesystem.root.getFile(path, {}, this.load.bind(this), error.bind(null, "getFile " + path));
  }
};

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