How to access polymer when "this" becomes "that" - polymer

Question

I am trying to integrate dropzone.js and cloudinary into Polymer 1.0. It does work, but I am hitting a stumbling block on how to send the dynamic URL generated by Cloudinary back to Polymer so I can write that URL into Firebase. I am inside a function listening to dropzone events with the intention of using iron-signals to signal a different web component. "this" is now scoped to dropzone.js and not Polymer.
..resulting in "Uncaught TypeError: this.fire is not a function".
The code is below, I am trying to start the iron-signal based on listening the dropzone.js "success" event which provides access to the new image URL.
<link rel="stylesheet" href="../../../bower_components/dropzone/dist/min/dropzone.min.css">
<dom-module id="my-dropzone">
<style>
:host {
display: block;
}
div#my-dropzone-area {
max-width=300px;
height=300px;
border: 4px dashed blue;
}
</style>
<template>
<paper-button on-tap="startTheMessage">Test Fire!</paper-button>
<iron-signals on-iron-signal-hello="passTheMessage">
<div class="dropzone" id="my-dropzone-area">
<div class="fallback">
<input name="file" type="file" multiple />
</div>
</div>
</template>
</dom-module>
<script>
(function() {
Polymer({
is: 'my-dropzone',
ready: function() {
// access a local DOM element by ID using this.$
Dropzone.options.myDropzoneArea = {
paramName: 'file', // The name that will be used to transfer the file
maxFilesize: 10, // MB
uploadMultiple: false,
acceptedFiles: '.jpg,.png,.jpeg,.gif',
parallelUploads: 6,
addRemoveLinks: true,
url: 'https://api.cloudinary.com/v1_1/remarkable-ky/image/upload',
init: function() {
this.on('addedfile', function(file) {
console.log('Added file.');
console.log(file);
});
this.on('sending', function(file, xhr, formData) {
console.log('Sending file.');
formData.append('api_key', 0000000000000);
formData.append('timestamp', Date.now() / 1000);
formData.append('upload_preset', 'where-ky');
});
this.on('success', function(file, response) {
var baseURL = 'http://res.cloudinary.com/remarkable-ky/image/upload/';
var url = baseURL.concat(response.public_id);
console.log('Cloudinary URL: ', url);
this.fire('iron-signal', {
name: 'hello',
data: null
});
});
}
};
},
startTheMessage: function() {
this.fire('iron-signal', {
name: 'hello',
data: null
});
},
passTheMessage: function() {
alert("got it");
},
properties: {},
});
})();
</script>
<script src="../../../bower_components/dropzone/dist/min/dropzone.min.js"></script>

Answer 1

you can pass this into the function with the .bind() function.
this.on('success', function(file, response) {
var baseURL = 'http://res.cloudinary.com/remarkable-ky/image/upload/';
var url = baseURL.concat(response.public_id);
console.log('Cloudinary URL: ', url);
this.fire('iron-signal', {
name: 'hello',
data: null
});
}.bind(this));