add converted prototype code

src/editor/caret.js

@@ -0,0 +1,78 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export function getCaretPosition(editor) {
+    const sel = document.getSelection();
+    const atNodeEnd = sel.focusOffset === sel.focusNode.textContent.length;
+    let position = sel.focusOffset;
+    let node = sel.focusNode;
+
+    // when deleting the last character of a node,
+    // the caret gets reported as being after the focusOffset-th node,
+    // with the focusNode being the editor
+    if (node === editor) {
+        let position = 0;
+        for (let i = 0; i < sel.focusOffset; ++i) {
+            position += editor.childNodes[i].textContent.length;
+        }
+        return {position, atNodeEnd: false};
+    }
+
+    // first make sure we're at the level of a direct child of editor
+    if (node.parentElement !== editor) {
+        // include all preceding siblings of the non-direct editor children
+        while (node.previousSibling) {
+            node = node.previousSibling;
+            position += node.textContent.length;
+        }
+        // then move up
+        // I guess technically there could be preceding text nodes in the parents here as well,
+        // but we're assuming there are no mixed text and element nodes
+        while (node.parentElement !== editor) {
+            node = node.parentElement;
+        }
+    }
+    // now include the text length of all preceding direct editor children
+    while (node.previousSibling) {
+        node = node.previousSibling;
+        position += node.textContent.length;
+    }
+    {
+        const {focusOffset, focusNode} = sel;
+        console.log("selection", {focusOffset, focusNode, position, atNodeEnd});
+    }
+    return {position, atNodeEnd};
+}
+
+export function setCaretPosition(editor, caretPosition) {
+    if (caretPosition) {
+        let focusNode = editor.childNodes[caretPosition.index];
+        if (!focusNode) {
+            focusNode = editor;
+        } else {
+            // make sure we have a text node
+            if (focusNode.nodeType === Node.ELEMENT_NODE) {
+                focusNode = focusNode.childNodes[0];
+            }
+        }
+        const sel = document.getSelection();
+        sel.removeAllRanges();
+        const range = document.createRange();
+        range.setStart(focusNode, caretPosition.offset);
+        range.collapse(true);
+        sel.addRange(range);
+    }
+}