Send {expr} over {handle}. The {expr} is encoded according to the type of channel. The function cannot be used with a raw channel. See |channel-use|. {handle} can be a Channel or a Job that has a Channel. {options} must be a Dictionary. It must not have a "callback" entry. It can have a "timeout" entry to specify the timeout for this specific request. ch_evalexpr() waits for a response and returns the decoded expression. When there is an error or timeout it returns an empty string. Note that while waiting for the response, Vim handles other messages. You need to make sure this doesn't cause trouble. Can also be used as a |method|: GetChannel()->ch_evalexpr(expr)