Codemod to replace the first block scope in a file by a IIFE

rename-element-to-polymerelement.js

export default function(file, api) {
  const j = api.jscodeshift;

  return j(file.source)
    .find(j.VariableDeclarator, {
      id: {
        type: 'Identifier',
        name: 'Element',
      },
    })
    .replaceWith(nodePath => {
      const { node } = nodePath;
      node.id.name = 'PolymerElement';
      return node;
    })
    .toSource();
}

transform-block-scope-to-iife.js

export default function(file, api) {
  const j = api.jscodeshift;

  return j(file.source)
    .find(j.BlockStatement)
    .at(0)
    .replaceWith(nodePath => {
      const nodeValue = nodePath.value;

      return j.expressionStatement(
        j.callExpression(
          j.functionExpression(null, [], j.blockStatement(nodeValue.body)),
          []
        )
      )
    }
  )
  .toSource();
}

Transforms the following code:

{
  const { Element, html } = Polymer;
}

To:

(function () {
  const { Element, html } = Polymer;
})();

Only the first block statement is replaced.