[Vuejs]-How to be warned when jwt expires?

Check if the token has expired when you load the token from local storage, but before you set the token within the application’s state:

let token = localStorage.getItem("token")
let payload = jwtDecode(token)

// payload.exp should contain the expiration epoch set upon creation
if (payload.exp > Math.round(Date.now() / 1000)) {
  alert("Your token has expired!")
}

If you do not have an expiration field but have an “issued-at” (iat) field, the following logic will also suffice for checking if it has been 30 minutes since it was issued:

const TIME_DELTA = 30 * 60 * 1000; // convert 30 minutes to epoch time 
if (payload.iat + TIME_DELTA <= Math.round(Date.now() / 1000)) {
  alert("Your token was issued more than 30 minutes ago!")
}