IE 11 - why is there an error in the method declaration?

Question

JavaScript

In IE 11, this error appears:

Swears at the line with the handler function inside the watch function , which is inside the Vue application:

// v.1
  watch: {
    numbers:  {
     handler(val, oldVal)  {
        // some code
      },
       deep: true
    }
 }

If you change the code to the following, then there is no error, but then tracking numbers does not work.

// v.2
  watch:  {
   numbers: function (val):  {                    
      // some code
   }                  
}

How to make the first option work in IE?

Answer 1

IE doesn't understand methods , write as a property with a function.

watch: {
    numbers:  {
     handler: function(val, oldVal)  {
        // some code
      },
       deep: true
    }
 }