diff --git a/src/static/js/Changeset.js b/src/static/js/Changeset.js
index 5d4871c5e..2b0e82482 100644
--- a/src/static/js/Changeset.js
+++ b/src/static/js/Changeset.js
@@ -184,11 +184,54 @@ exports.newLen = (cs) => exports.unpack(cs).newLen;
  * Iterator over a changeset's operations.
  *
  * Note: This class does NOT implement the ECMAScript iterable or iterator protocols.
- *
- * @typedef {object} OpIter
- * @property {Function} hasNext -
- * @property {Function} next -
  */
+class OpIter {
+  /**
+   * @param {string} ops - String encoding the change operations to iterate over.
+   */
+  constructor(ops) {
+    this._ops = ops;
+    this._regex = /((?:\*[0-9a-z]+)*)(?:\|([0-9a-z]+))?([-+=])([0-9a-z]+)|(.)/g;
+    this._nextMatch = this._nextRegexMatch();
+  }
+
+  _nextRegexMatch() {
+    const match = this._regex.exec(this._ops);
+    if (!match) return null;
+    if (match[5] === '$') return null; // Start of the insert operation character bank.
+    if (match[5] != null) error(`invalid operation: ${this._ops.slice(this._regex.lastIndex - 1)}`);
+    return match;
+  }
+
+  /**
+   * @returns {boolean} Whether there are any remaining operations.
+   */
+  hasNext() {
+    return this._nextMatch && !!this._nextMatch[0];
+  }
+
+  /**
+   * Returns the next operation object and advances the iterator.
+   *
+   * Note: This does NOT implement the ECMAScript iterator protocol.
+   *
+   * @param {Op} [opOut] - Deprecated. Operation object to recycle for the return value.
+   * @returns {Op} The next operation, or an operation with a falsy `opcode` property if there are
+   *     no more operations.
+   */
+  next(opOut = new Op()) {
+    if (this.hasNext()) {
+      opOut.attribs = this._nextMatch[1];
+      opOut.lines = exports.parseNum(this._nextMatch[2] || '0');
+      opOut.opcode = this._nextMatch[3];
+      opOut.chars = exports.parseNum(this._nextMatch[4]);
+      this._nextMatch = this._nextRegexMatch();
+    } else {
+      clearOp(opOut);
+    }
+    return opOut;
+  }
+}
 
 /**
  * Creates an iterator which decodes string changeset operations.
@@ -196,38 +239,7 @@ exports.newLen = (cs) => exports.unpack(cs).newLen;
  * @param {string} opsStr - String encoding of the change operations to perform.
  * @returns {OpIter} Operator iterator object.
  */
-exports.opIterator = (opsStr) => {
-  const regex = /((?:\*[0-9a-z]+)*)(?:\|([0-9a-z]+))?([-+=])([0-9a-z]+)|(.)/g;
-
-  const nextRegexMatch = () => {
-    const result = regex.exec(opsStr);
-    if (!result) return null;
-    if (result[5] === '$') return null; // Start of the insert operation character bank.
-    if (result[5] != null) error(`invalid operation: ${opsStr.slice(regex.lastIndex - 1)}`);
-    return result;
-  };
-  let regexResult = nextRegexMatch();
-
-  const hasNext = () => regexResult && !!regexResult[0];
-
-  const next = (op = new Op()) => {
-    if (hasNext()) {
-      op.attribs = regexResult[1];
-      op.lines = exports.parseNum(regexResult[2] || '0');
-      op.opcode = regexResult[3];
-      op.chars = exports.parseNum(regexResult[4]);
-      regexResult = nextRegexMatch();
-    } else {
-      clearOp(op);
-    }
-    return op;
-  };
-
-  return {
-    next,
-    hasNext,
-  };
-};
+exports.opIterator = (opsStr) => new OpIter(opsStr);
 
 /**
  * Cleans an Op object.
@@ -352,7 +364,7 @@ exports.checkRep = (cs) => {
   let oldPos = 0;
   let calcNewLen = 0;
   let numInserted = 0;
-  const iter = exports.opIterator(ops);
+  const iter = new OpIter(ops);
   while (iter.hasNext()) {
     const o = iter.next();
     switch (o.opcode) {
@@ -1005,8 +1017,8 @@ class TextLinesMutator {
  * @returns {string} the integrated changeset
  */
 const applyZip = (in1, in2, func) => {
-  const iter1 = exports.opIterator(in1);
-  const iter2 = exports.opIterator(in2);
+  const iter1 = new OpIter(in1);
+  const iter2 = new OpIter(in2);
   const assem = exports.smartOpAssembler();
   const op1 = new Op();
   const op2 = new Op();
@@ -1075,7 +1087,7 @@ exports.pack = (oldLen, newLen, opsStr, bank) => {
 exports.applyToText = (cs, str) => {
   const unpacked = exports.unpack(cs);
   assert(str.length === unpacked.oldLen, `mismatched apply: ${str.length} / ${unpacked.oldLen}`);
-  const csIter = exports.opIterator(unpacked.ops);
+  const csIter = new OpIter(unpacked.ops);
   const bankIter = exports.stringIterator(unpacked.charBank);
   const strIter = exports.stringIterator(str);
   const assem = exports.stringAssembler();
@@ -1120,7 +1132,7 @@ exports.applyToText = (cs, str) => {
  */
 exports.mutateTextLines = (cs, lines) => {
   const unpacked = exports.unpack(cs);
-  const csIter = exports.opIterator(unpacked.ops);
+  const csIter = new OpIter(unpacked.ops);
   const bankIter = exports.stringIterator(unpacked.charBank);
   const mut = new TextLinesMutator(lines);
   while (csIter.hasNext()) {
@@ -1251,7 +1263,7 @@ exports.applyToAttribution = (cs, astr, pool) => {
 
 exports.mutateAttributionLines = (cs, lines, pool) => {
   const unpacked = exports.unpack(cs);
-  const csIter = exports.opIterator(unpacked.ops);
+  const csIter = new OpIter(unpacked.ops);
   const csBank = unpacked.charBank;
   let csBankIndex = 0;
   // treat the attribution lines as text lines, mutating a line at a time
@@ -1265,7 +1277,7 @@ exports.mutateAttributionLines = (cs, lines, pool) => {
   const nextMutOp = () => {
     if ((!(lineIter && lineIter.hasNext())) && mut.hasMore()) {
       const line = mut.removeLines(1);
-      lineIter = exports.opIterator(line);
+      lineIter = new OpIter(line);
     }
     if (!lineIter || !lineIter.hasNext()) return new Op();
     return lineIter.next();
@@ -1328,7 +1340,7 @@ exports.mutateAttributionLines = (cs, lines, pool) => {
 exports.joinAttributionLines = (theAlines) => {
   const assem = exports.mergingOpAssembler();
   for (const aline of theAlines) {
-    const iter = exports.opIterator(aline);
+    const iter = new OpIter(aline);
     while (iter.hasNext()) {
       assem.append(iter.next());
     }
@@ -1337,7 +1349,7 @@ exports.joinAttributionLines = (theAlines) => {
 };
 
 exports.splitAttributionLines = (attrOps, text) => {
-  const iter = exports.opIterator(attrOps);
+  const iter = new OpIter(attrOps);
   const assem = exports.mergingOpAssembler();
   const lines = [];
   let pos = 0;
@@ -1495,7 +1507,7 @@ const toSplices = (cs) => {
   const splices = [];
 
   let oldPos = 0;
-  const iter = exports.opIterator(unpacked.ops);
+  const iter = new OpIter(unpacked.ops);
   const charIter = exports.stringIterator(unpacked.charBank);
   let inSplice = false;
   while (iter.hasNext()) {
@@ -1742,7 +1754,7 @@ exports.copyAText = (atext1, atext2) => {
  */
 exports.opsFromAText = function* (atext) {
   // intentionally skips last newline char of atext
-  const iter = exports.opIterator(atext.attribs);
+  const iter = new OpIter(atext.attribs);
   let lastOp = null;
   while (iter.hasNext()) {
     if (lastOp != null) yield lastOp;
@@ -1964,7 +1976,7 @@ exports.makeAttribsString = (opcode, attribs, pool) => {
  * Like "substring" but on a single-line attribution string.
  */
 exports.subattribution = (astr, start, optEnd) => {
-  const iter = exports.opIterator(astr);
+  const iter = new OpIter(astr);
   const assem = exports.smartOpAssembler();
   let attOp = new Op();
   const csOp = new Op();
@@ -2033,13 +2045,13 @@ exports.inverse = (cs, lines, alines, pool) => {
   let curLineNextOp = new Op('+');
 
   const unpacked = exports.unpack(cs);
-  const csIter = exports.opIterator(unpacked.ops);
+  const csIter = new OpIter(unpacked.ops);
   const builder = exports.builder(unpacked.newLen);
 
   const consumeAttribRuns = (numChars, func /* (len, attribs, endsLine)*/) => {
     if ((!curLineOpIter) || (curLineOpIterLine !== curLine)) {
       // create curLineOpIter and advance it to curChar
-      curLineOpIter = exports.opIterator(alinesGet(curLine));
+      curLineOpIter = new OpIter(alinesGet(curLine));
       curLineOpIterLine = curLine;
       let indexIntoLine = 0;
       while (curLineOpIter.hasNext()) {
@@ -2058,7 +2070,7 @@ exports.inverse = (cs, lines, alines, pool) => {
         curChar = 0;
         curLineOpIterLine = curLine;
         curLineNextOp.chars = 0;
-        curLineOpIter = exports.opIterator(alinesGet(curLine));
+        curLineOpIter = new OpIter(alinesGet(curLine));
       }
       if (!curLineNextOp.chars) {
         curLineNextOp = curLineOpIter.hasNext() ? curLineOpIter.next() : new Op();