+ * TODO(danvk): use @template here when it's better supported for classes.
+ * @param {!Array} array
+ * @param {number} start
+ * @param {number} length
+ * @param {function(!Array,?):boolean=} predicate
+ * @constructor
+ */
+Dygraph.Iterator = function(array, start, length, predicate) {
+ start = start || 0;
+ length = length || array.length;
+ this.hasNext = true; // Use to identify if there's another element.
+ this.peek = null; // Use for look-ahead
+ this.start_ = start;
+ this.array_ = array;
+ this.predicate_ = predicate;
+ this.end_ = Math.min(array.length, start + length);
+ this.nextIdx_ = start - 1; // use -1 so initial advance works.
+ this.next(); // ignoring result.
+};
+
+/**
+ * @return {Object}
+ */
+Dygraph.Iterator.prototype.next = function() {
+ if (!this.hasNext) {
+ return null;
+ }
+ var obj = this.peek;
+
+ var nextIdx = this.nextIdx_ + 1;
+ var found = false;
+ while (nextIdx < this.end_) {
+ if (!this.predicate_ || this.predicate_(this.array_, nextIdx)) {
+ this.peek = this.array_[nextIdx];
+ found = true;
+ break;
+ }
+ nextIdx++;
+ }
+ this.nextIdx_ = nextIdx;
+ if (!found) {
+ this.hasNext = false;
+ this.peek = null;
+ }
+ return obj;
+};
+
+/**
+ * Returns a new iterator over array, between indexes start and
+ * start + length, and only returns entries that pass the accept function
+ *
+ * @param {!Array} array the array to iterate over.
+ * @param {number} start the first index to iterate over, 0 if absent.
+ * @param {number} length the number of elements in the array to iterate over.
+ * This, along with start, defines a slice of the array, and so length
+ * doesn't imply the number of elements in the iterator when accept doesn't
+ * always accept all values. array.length when absent.
+ * @param {function(?):boolean=} opt_predicate a function that takes
+ * parameters array and idx, which returns true when the element should be
+ * returned. If omitted, all elements are accepted.