hello != jello

> I can't have any meaningfull result ...

Which error message do you get?

I don't have phantomjs installed, so please provide a reproducible example.

UPDATE

I ran your JS code in the browser's console and it works for me:

> var leg = {
aa: "Hello from javascript"
}

function to_json() {
   return JSON.stringify(leg);
}

< undefined

> JSON.stringify(leg);

< "{\"aa\":\"Hello from javascript\"}"

> to_json()

< "{\"aa\":\"Hello from javascript\"}"
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