What does this entry .trigger('update') mean in jquery?

Question

JavaScript

And if possible, this is of interest to .on ('update')

Answer 1

Obviously, clumsy json is coming. Output xmlhttp.responseText to the console and look at it either with your eyes or with some online parser that will show where the error is.
UPD:
And in general:

var response = xmlhttp.responseText;
response = JSON.parse(response);

why not:

var response =  JSON.parse( xmlhttp.responseText );

Answer 2

Real life example:
When the green light at the traffic light turns on, the cars go - this is on('greenlight', function(){ cars.go(); })
And for the cars to go, you can force the green light to turn on - thistrigger('greenlight')

Answer 3

And if possible, this is of interest

and if possible, there is a dock + TONS of articles on the Internet
google jquery on
Results: about
54,800,000 YOU ARE NOT ENOUGH WHAT YOU STILL ASK???????????????????????? ???????