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# `macro()` The macro method lets you register custom methods ```js collect().macro('uppercase', function () { return this.map(item => item.toUpperCase()); }); const collection = collect(['a', 'b', 'c']); collection.uppercase(); collection.all(); // ['A', 'B', 'C'] ``` > Note that the `macro` method returns `undefined`, and therefore it is not possible to use it within a chain of methods. [View source on GitHub](https://github.com/ecrmnn/collect.js/blob/master/src/methods/macro.js)