client/web/app.js

var vibrateInterval;

function vibrate(flutter_value) {
    clearInterval(vibrateInterval);  

    if ("vibrate" in navigator){
        // alert("supported");
        navigator.vibrate(flutter_value);
    }
}

function sum(arr1){
    if(arr1.constructor !== Array)   return arr1
    
    function add(accumulator, a) {
      return accumulator + a;
    }
    sumvalue = arr1.reduce(add, 0);
    return sumvalue;
}

function setIntervalAndExecute(fn, t) {
    fn();
    return(setInterval(fn, t));
}

function peristentVibrate(pattern) {
    
    // alert("supported");
    // vibrateInterval = setInterval(() => {
    vibrateInterval = setIntervalAndExecute(() => {
        if ("vibrate" in navigator){
            navigator.vibrate(pattern);
        }
    }, sum(pattern));
        
}