How to use the parchment.Leaf function in parchment

format(format, value) {
    this.scroll.update();
    let nativeRange = this.getNativeRange();
    if (nativeRange == null || !nativeRange.native.collapsed || Parchment.query(format, Parchment.Scope.BLOCK)) return;
    if (nativeRange.start.node !== this.cursor.textNode) {
      let blot = Parchment.find(nativeRange.start.node, false);
      if (blot == null) return;
      // TODO Give blot ability to not split
      if (blot instanceof Parchment.Leaf) {
        let after = blot.split(nativeRange.start.offset);
        blot.parent.insertBefore(this.cursor, after);
      } else {
        blot.insertBefore(this.cursor, nativeRange.start.node);  // Should never happen
      }
      this.cursor.attach();
    }
    this.cursor.format(format, value);
    this.scroll.optimize();
    this.setNativeRange(this.cursor.textNode, this.cursor.textNode.data.length);
    this.update();
  }

import Parchment from 'parchment';


class Cursor extends Parchment.Leaf {
  constructor(domNode, selection) {
    super(domNode);
    this.selection = selection;
    this.textNode = document.createTextNode(Cursor.CONTENTS);
    this.domNode.appendChild(this.textNode);
    this._length = 0;
  }

  format(name, value) {
    if (this._length !== 0) {
      return super.format(name, value);
    }
    let target = this, index = 0;
    this._length = Cursor.CONTENTS.length;
    while (target != null && target.statics.scope !== Parchment.Scope.BLOCK_BLOT) {
      index += target.offset(target.parent);