How can I export all functions from a file in JS?

No, there’s no wildcard export (except when you’re re-exporting everything from another module, but that’s not what you’re asking about).

Simply put export in front of each function declaration you want exported, e.g.

export function foo() {
    // ...
}
export function bar() {
    // ...
}

…or of course, if you’re using function expressions:

export var foo = function() {
    // ...
};
export let bar = () => {
    // ...
};
export const baz = value => {
    // ...
};