let self = this;
let filter = document.querySelector('input.filter');
filter.value = '';
this.returnedArr = [];
filter.oninput = function(event) {
    self.returnedArr = self.searchArr.concat(self.discardedArr);
    if (event.target.value === '') {
        self.tableRender(self.returnedArr);  //undefined. Как исправить?
    }
};