src/language-js/parse/postprocess/typescript.js/throwErrorForInvalidAbstractProperty
function throwErrorForInvalidAbstractProperty(tsNode, esTreeNode) {
  const SYNTAX_KIND_PROPERTY_DEFINITION = 167;
  const SYNTAX_KIND_ABSTRACT_KEYWORD = 126;
  if (
    tsNode.kind !== SYNTAX_KIND_PROPERTY_DEFINITION ||
    (tsNode.modifiers &&
      !tsNode.modifiers.some(
        (modifier) => modifier.kind === SYNTAX_KIND_ABSTRACT_KEYWORD
      ))
  ) {
    return;
  }
  if (tsNode.initializer && esTreeNode.value === null) {
    throwSyntaxError(
      esTreeNode,
      "Abstract property cannot have an initializer"
    );
  }
}