/**
 * Function to remove duplicate items, using "key" as comparison (other keys are not considered)
 */
function ereUniques(arr, key) {
	var len = arr.length;
	var seen = [];
	var final = [];
	var finalCounter = 0;
	var i, innerItem;
	for (i = 0; i < len; i++) {
		innerItem = arr[i][key];
		if (seen[innerItem] !== 1) {
			seen[innerItem] = 1;
			final[finalCounter++] = arr[i];
		}
	}
	return final;
}



//test array (last two elements have the same "date")
var testArray = [{"date":"2018-05-22T14:01:25+00:00","wtt":"93.7314"},{"date":"2018-05-22T16:38:25+00:00","wtt":"94.0171"},{"date":"2018-05-22T16:38:25+00:00","wtt":"94.0171"}];
var result = ereUniques(testArray, 'date');

//result should be
//[{"date":"2018-05-22T14:01:25+00:00","wtt":"93.7314"},{"date":"2018-05-22T16:38:25+00:00","wtt":"94.0171"}]