function onCommand() {
		var action;
		var nargs;

		nargs = arguments.length;
		if ( nargs === 0 ) {
			return repl.keybindings();
		}
		if ( nargs === 1 ) {
			action = arguments[ 0 ];
			if ( !isString( action ) ) {
				repl._ostream.write( format( 'Error: invalid argument. First argument must be a string. Value: `%s`.', action ) );
				return;
			}
			if ( !isAction( action ) ) {
				repl._ostream.write( format( 'Error: invalid argument. First argument must be a valid action name. Value: `%s`.', action ) );
				return;
			}
			return repl.keybindings()[ action ];
		}
	}
Returns all (or select) keybindings.

@private
@param {string} [action] - action name
@returns {(Object|Array<Object>)} keybindings object or a list of keybindings