Allow esc key to hide multiselect options

[jhudson8]

Clicking on a canvas element will not hide the multiselect options. If most of the page is a canvas element this makes things difficult.

It would be great if the esc key would hide the multiselect menu. I think it would be fairly simple (although I haven't been in the code much)

Handle key down event to detect when escape key is clicked
https://github.com/palantir/blueprint/blob/develop/packages/select/src/components/select/multiSelect.tsx#L140

Set state isOpen to false and blur the input field

Thanks

[giladgray]

oh yeah seems it's trying to close on escape (from Popover), but the input focus re-opens it. eas to fix, as you suggested above.

[danielbh]

This is very straightforward as you said. You can just put a this.input.blur() here. However, I'm having trouble creating test coverage. What I was thinking was just to put a test spy on onBlur, but I'm having trouble accessing the event. What do you recommend?

[giladgray]

@danielbh the select package does not have coverage requirements so don't bother too hard with tests. would love to see your change, please push it up to a branch and set up CircleCI!