Calm down, take a deep breath, let's go by parties brother, first things first, the arrow functions were created to save equivalent code (so to speak).
return availability.price && availability.options.filter(function(x){ x.leadTime >= 0}).length > 0;
With regard to the second, this will work for you:
.then(function (result) { console.log(result); })
.finally(function () {
$window.location.reload();
});
Generally:
If you find a function like arrow (arrow) and want to send it to be compatible with IE 11, simply add the magic word function followed by the name of the variable as a parameter and in the case that it does not have as in the line of .finally , just add function() . Of course, remember to delete the arrow => and have the start keys { and close } well placed.
If you want a better way to program using JavaScript and that your code is adapted to lower version browsers, I recommend using link