constructor({body, params, defaults, rest, async}) {
    super('ArrowFunctionExpression');

    this.body = body;
    this.params = params;
    this.defaults = defaults;
    this.rest = rest;
    this.async = async;
    this.generator = false;
    this.id = undefined;
  }
The constructor of ArrowFunctionExpression

@param {Object} cfg
@param {Node} cfg.body
@param {Node[]} cfg.params
@param {Node[]} cfg.defaults
@param {Node} cfg.rest (optional)