Try passing the jQuery object as a parameter to the other modules:
export function exmain ($) {
'use strict';
var a= "hello main";
alert (a);
function one() {
//..
}
}
export function exhelp ($) {
'use strict';
var msg='hello module';
function two() {
//..
}
$('.toast-msg').text('msg');
}
import {exmain} from './main.js'
import {exhelp} from './apphelp.js'
(function ($) {
exmain($);
exhelp($);
})(jQuery);