When user listens click event using:
chart.on('click', function() {...})
It only receives message when the click is on the series item.
In the case of line charts, it only triggers when clicks on the small
symbol on the line.
But for line charts that with axisPointer or tooltip of 'axis' type (e.g.:
http://gallery.echartsjs.com/editor.html?c=xSJfK8-MCo&v=2 ), this may not
make sense.
It is expected that click event is triggered whenever clicking inside grid
area, or maybe whenever tooltip or axisPointer is shown.
This is extremely useful on mobile since currently click can almost never
triggered except that touch exactly on the symbol item.
Another thing is, it is also often requested that clicks on other
components, like axis label, title, and etc. should also be triggered and
can be listened by users.
Zhang Wenli
http://zhangwenli.com
