got “Unexpected token import” on code compiled with @vitejs/plugin-legacy

[mis98zb]

I tried to use @vitejs/plugin-legacy to compile code for chrome 49.
Below is my setting in viteconfig.js:
const legacyOption = {
targets: ['Chrome >= 49', 'Firefox >= 52'],
}

export default ({ command, mode }) => {
return {
root,
resolve,
server,
css,
//build,
plugins: [
vue(),
legacy(legacyOption)
],
}
}

Compile finished without error. However, when I open the website and login, on page routing I got several errors:
Uncaught SyntaxError: Unexpected token import
polyfills-legacy.6efd4eb6.js:1 Unhandled promise rejection SyntaxError: Unexpected token import(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Uo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1lo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Ui.(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Mi @ polyfills-legacy.6efd4eb6.js:1Fi @ polyfills-legacy.6efd4eb6.js:1
polyfills-legacy.6efd4eb6.js:1 Unhandled promise rejection TypeError: Illegal invocation(…)(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Uo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1lo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Ui.(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Mi @ polyfills-legacy.6efd4eb6.js:1Fi @ polyfills-legacy.6efd4eb6.js:1
resize-event-legacy.697e0ca5.js:1 Uncaught SyntaxError: Unexpected token import
polyfills-legacy.6efd4eb6.js:1 Unhandled promise rejection SyntaxError: Unexpected token import(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Uo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1lo @ polyfills-legacy.6efd4eb6.js:1(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Ui.(anonymous function) @ polyfills-legacy.6efd4eb6.js:1Mi @ polyfills-legacy.6efd4eb6.js:1Fi @ polyfills-legacy.6efd4eb6.js:1
polyfills-legacy.6efd4eb6.js:1 Unhandled promise rejection SyntaxError: Unexpected token import

Can anybody help to figure out how to solve this?
Appreciate for any hint...