Safari browser compatibility

1) Avoid using let for variable declaration use var 
let x=10; or const x=10;
var x=10; (compatibale)

2) Avoid using default value for funcation parameter
function add(a,b=20){
}

//instead use this way
funcation add(a,b){
  var b;
  if (typeof b === "undefined") { b = 20; }
}

3) Avoid using arrow funcation
hello = () => {
  return "Hello World!";
}

4) Avoid javacript template string like  (don't use ``)
`this is template string ${xvriable} eclosed in backquote `

5) this will help to convert ES6 to ES5 https://babeljs.io/repl

6) old iphone when using div with onclick=""
must add css: cursor: pointer;