[Vue warn]: Error in render: "TypeError: discountReviews[i] is undefined"

getAverage: function(discount){


        let discountReviews = discount.discountreviews;

        if(discountReviews.length == 0){
            return 5;
        }
        else{
            let total = 0;
            console.log(discountReviews.length);
            for(var i=0; i<= discountReviews.length; i++){
                total = parseInt(total) + parseInt( discountReviews[i].rating);
            }

            let average = Math.ceil(total / discountReviews.length);

            return average;

        }

    },