kernel.js

const extra_map = (notebook, cell) => ({
        ['Alt--'](cm) {
                cm.replaceSelection(' <- ')
        },
        ['Shift-Ctrl-M'](cm) {
                cm.replaceSelection(' %>% ')
        },
        F1(cm) {
                const {anchor, head} = cm.findWordAt(cm.getCursor())
                const word = cm.getRange(anchor, head)

                const callbacks = cell.get_callbacks()
                const options = {silent: false, store_history: false, stop_on_error: true}
                cell.last_msg_id = notebook.kernel.execute(`help(${word})`, callbacks, options) 
        },
})

function enable_extra_keys(notebook, cell) {
        if (!cell.code_mirror) return
        const old_keymap = cell.code_mirror.getOption('extraKeys')
        const new_keymap = Object.assign({}, old_keymap, extra_map(notebook, cell))
        cell.code_mirror.setOption('extraKeys', new_keymap)
}

define(['base/js/namespace'], ({notebook}) => ({
        onload() {
                for (let cell of notebook.get_cells())
                        enable_extra_keys(notebook, cell)

                notebook.events.on('edit_mode.Cell', (event, {cell}) =>
                        enable_extra_keys(notebook, cell))
        },
}))