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diff --git a/app/assets/javascripts/issues/show/utils.js b/app/assets/javascripts/issues/show/utils.js
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+++ b/app/assets/javascripts/issues/show/utils.js
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+import { COLON, HYPHEN, NEWLINE } from '~/lib/utils/text_utility';
+
+/**
+ * Get the index from sourcepos that represents the line of
+ * the description when the description is split by newline.
+ *
+ * @param {String} sourcepos Source position in format `23:3-23:14`
+ * @returns {Number} Index of description split by newline
+ */
+const getDescriptionIndex = (sourcepos) => {
+  const [startRange] = sourcepos.split(HYPHEN);
+  const [startRow] = startRange.split(COLON);
+  return startRow - 1;
+};
+
+/**
+ * Given a `ul` or `ol` element containing a new sort order, this function performs
+ * a depth-first search to get the new sort order in the form of sourcepos indices.
+ *
+ * @param {HTMLElement} list A `ul` or `ol` element containing a new sort order
+ * @returns {Array<Number>} An array representing the new order of the list
+ */
+const getNewSourcePositions = (list) => {
+  const newSourcePositions = [];
+
+  function pushPositionOfChildListItems(el) {
+    if (!el) {
+      return;
+    }
+    if (el.tagName === 'LI') {
+      newSourcePositions.push(getDescriptionIndex(el.dataset.sourcepos));
+    }
+    Array.from(el.children).forEach(pushPositionOfChildListItems);
+  }
+
+  pushPositionOfChildListItems(list);
+
+  return newSourcePositions;
+};
+
+/**
+ * Converts a description to one with a new list sort order.
+ *
+ * Given a description like:
+ *
+ * <pre>
+ * 1. I am text
+ * 2.
+ * 3. - Item 1
+ * 4. - Item 2
+ * 5.   - Item 3
+ * 6.   - Item 4
+ * 7. - Item 5
+ * </pre>
+ *
+ * And a reordered list (due to dragging Item 2 into Item 1's position) like:
+ *
+ * <pre>
+ * <ul data-sourcepos="3:1-8:0">
+ *   <li data-sourcepos="4:1-4:8">
+ *     Item 2
+ *     <ul data-sourcepos="5:1-6:10">
+ *       <li data-sourcepos="5:1-5:10">Item 3</li>
+ *       <li data-sourcepos="6:1-6:10">Item 4</li>
+ *     </ul>
+ *   </li>
+ *   <li data-sourcepos="3:1-3:8">Item 1</li>
+ *   <li data-sourcepos="7:1-8:0">Item 5</li>
+ * <ul>
+ * </pre>
+ *
+ * This function returns:
+ *
+ * <pre>
+ * 1. I am text
+ * 2.
+ * 3. - Item 2
+ * 4.   - Item 3
+ * 5.   - Item 4
+ * 6. - Item 1
+ * 7. - Item 5
+ * </pre>
+ *
+ * @param {String} description Description in markdown format
+ * @param {HTMLElement} list A `ul` or `ol` element containing a new sort order
+ * @returns {String} Markdown with a new list sort order
+ */
+export const convertDescriptionWithNewSort = (description, list) => {
+  const descriptionLines = description.split(NEWLINE);
+  const startIndexOfList = getDescriptionIndex(list.dataset.sourcepos);
+
+  getNewSourcePositions(list)
+    .map((lineIndex) => descriptionLines[lineIndex])
+    .forEach((line, index) => {
+      descriptionLines[startIndexOfList + index] = line;
+    });
+
+  return descriptionLines.join(NEWLINE);
+};