Mapbox GL JS : Popup onclick with external JSON - geojson

Question

I am trying to display a popup onclick in Mapbox GL JS when the user clicks a polygon (It's a weather warning box during a Flash Flood Warning).
I have been using this example from Mapbox as a base, and -
This is my JSON file that I am trying to pull data from.
When I click the polygon, there is no popup. When I mouseover it, the cursor changes - so I know the basic possible issues like filename and directory structure are right.
My code below was modified from the example. I am trying to load the "description" of each polygon : (My map is called "topleftmapbox" and the JSON id is "FFWWarning")
// When a click event occurs on a feature in the places layer, open a popup at the
// location of the feature, with description HTML from its properties.
topleftmapbox.on('click', 'FFWWarning', function (e) {
var coordinates = e.features[0].geometry.coordinates.slice();
var description = e.features[0].description;
// Ensure that if the map is zoomed out such that multiple
// copies of the feature are visible, the popup appears
// over the copy being pointed to.
while (Math.abs(e.lngLat.lng - coordinates[0]) > 180) {
coordinates[0] += e.lngLat.lng > coordinates[0] ? 360 : -360;
}
new mapboxgl.Popup()
.setLngLat(coordinates)
.setHTML(description)
.addTo(topleftmapbox);
});
// The following code below runs correctly and changes the cursor on mouseover.
topleftmapbox.on('mouseenter', 'FFWWarning', function () {
topleftmapbox.getCanvas().style.cursor = 'pointer';
});
// Change it back to a pointer when it leaves.
topleftmapbox.on('mouseleave', 'FFWWarning', function () {
topleftmapbox.getCanvas().style.cursor = '';
});
I have a feeling that my issue is somewhere in this part of the code :
var coordinates = e.features[0].geometry.coordinates.slice();
var description = e.features[0].description;
I am still new with Mapbox and I have tried looking through here and various sources online to fix this. I am hoping the issue is just that I have the description variable set wrong and that I am missing something simple.

Answer 1

I debugged the code that you provided and found that variable coordinates was containing an object having array of lat-lng.
Modifying that part should fix the issue.
var coordinates = e.features[0].geometry.coordinates[0][0].slice();
In coordinates[0][0], second index determines the position of popup.
Here is the working code. https://jsbin.com/suzapug/1/edit?html,output