babel-plugin-demo

// babel plugin
export default function (babel) {
  const { types: t } = babel;

  return {
    name: 'ast-transform', // not required
    visitor: {
      Identifier(path) {
        // path.node.name = path.node.name.split('').reverse().join('');
        //const parentPath = path.findParent((path) => path.isFunctionDeclaration());
        //console.log('ttt', parentPath);
        //if (parentPath) {
        //  const param = parentPath.node.params.find((p) => p.name === path.node.name && t.isIdentifier(p));
        //  if (param) {
        //    param.name = 'a';
        //  }
        //}
      },
      ArrayExpression(path) {
        path.node.elements.push(t.numberLiteral(10));
      },
      NumericLiteral(path) {
        if (
          path.node.value === 2 &&
          path.findParent((path) => path.isIfStatement())
        ) {
          path.node.value *= 10;
        }
      },

      FunctionDeclaration(path) {
        const paramsNames = path.node.params.map((item) => {
          if (t.isIdentifier(item)) {
            return item.name;
          }

          if (t.isAssignmentPattern) {
            return item.left.name;
          }
        });

        const pPrefix = 'a';

        path.stop();

        path.traverse({
          Identifier(path) {
            console.log('f_i', path.node);
            paramsNames.forEach((p, index) => {
              if (path.node.name === p) {
                path.node.name = `${pPrefix}${index}`;
                path.node.end -= 1;
              }
            });
          },
        });
      },

      ArrowFunctionExpression(path) {
        const { node } = path;
        console.log('arrow', path);
        const blockStatement = t.isBlockStatement(node.body)
          ? node.body
          : t.blockStatement([t.returnStatement(node.body)]);
        path.replaceWith(
          t.functionExpression(
            null,
            node.params,
            blockStatement,
            node.generator,
            node.async
          )
        );
      },
    },
  };
}