I often use Vimium in Chrome to search bookmarks. Some bookmarks are Chinese and some are English, so I need to switch input methods. I noticed Vimium searches in real time based on input characters, regardless of whether an IME is in use. I hadn’t encountered this in development, so I decided to understand it properly.
Can JS get the current input method name or temporarily switch input method?
The answer is no for both. JS cannot access input method information, nor can it change it. Some pages can prompt whether you’re in Chinese/English input mode by observing input events and characters.
What about Chrome extensions like Vimium? Besides JS, extensions have some Chrome App capabilities, but they still cannot modify input methods.
Input events in JS: input and composition
In JS there are these events:
- input
- composition
- compositionstart / compositionupdate / compositionend
Whenever a user inputs something, the input event fires. Even with a Chinese IME, input fires in real time.
Composition events only fire when using IMEs or other multi-key character input. They trigger compositionstart, compositionupdate, and compositionend in sequence.
Vimium listens to input events, which is why it keeps searching continuously.
Note: InputEvent has an isComposing property, which tells you whether you are currently composing (e.g., in a Chinese IME). This is very useful.
My understanding
Input can be direct or indirect. For English words, keyboard input is the final output. For Chinese, you type weixin and then the IME converts it to wechat. That is indirect/composed input. This explains why JS has composition events.
