Welcome to an advanced whirlwind tour through the powerful aspects of TypeScript. For those of us who’ve been enjoying the JavaScript world, TypeScript has added another layer of reliability, predictability, and functionality to our code. However, to truly power-up your development, understanding the advanced concepts of TypeScript is crucial. This tutorial serves that purpose - illuminating the path for experienced developers towards achieving mastery of TypeScript.

We will be delving into complex types, conditional types, mapped types, utilizing real-world code examples from TypeScript GitHub repository.

1. Complex Types

In TypeScript, you can create complex types by combining existing data types. You can use | to denote a Union type, which can be of either type, and & to denote an Intersection type, combining multiple types.

type ComplexType = TypeA & TypeB;
type UnionType = TypeA | TypeB;

Be aware, Union types may lead to certain gotchas, for instance, when each type in the union has a unique set of properties.

2. Conditional Types

Introduced in TypeScript 2.8, conditional types are an innovative tool for code branching.

In essence, they are a form of TypeScript’s syntax for expressing types in a flexible, compositional manner. They can take the form T extends U ? X : Y.

type LargerType<T> = T extends number[] ? 'Array of numbers' : 'Other Type';
type result = LargerType<number[]>;  // 'Array of numbers'

Discriminant properties are often used with conditional types, further boosting their power.

3. Mapped Types

A significant feature of TypeScript 2.1, mapped types allows you to create a new type based on the modifiers or transformations applied to each property of an existing type.

Let’s consider a classic example of transforming all properties of a type into optional properties:

// Original Product type
type Product = {
  id: number;
  name: string;
  price: number;
};

// Using Mapped Types
type OptionalProduct = {
  [K in keyof Product]?: Product[K]
};

// OptionalProduct now is equivalent to:
// type OptionalProduct = {
//     id?: number;
//     name?: string;
//     price?: number;
// }

Watch out for the adamant gotcha - if you apply a mapped type to an intersection type, the properties of the outcome may not behave as expected.

As what Anders Hejlsberg, the original designer of C#, says - “The key to TypeScript is that it lets you write the JavaScript you want to write. With TypeScript, we’re trying to provide a tool that aids productivity with superpowers.”

That’s exactly why these advanced features and more empower JavaScript developers with the robustness and expressiveness that leads to cleaner, less prone-to-error code, and ultimately, more elaborate software.

These advanced aspects can be daunting at first sight, their functionality allows for an increase in productivity, maintenance, and general code quality over time. So, approach them as an exciting adventure into the depth of TypeScript.

Reviewing open-source TypeScript projects on GitHub, such as Babylon.js, Ionic, and Nest.js, can provide inspiration and concrete examples of advanced TypeScript in action.

In essence, TypeScript adds a solid foundational structure that JavaScript inherently lacks. Its advanced features help developers deal with complex data structures, handle edge cases, and improve codebase scalability. Regardless of the learning curve, the trade-off pays off long-term.

Just remember, as renowned software engineer Robert C. Martin once said, “The only way to go fast is to go well.” Learn these advanced TypeScript concepts well, and your speed and efficiency in coding will inevitably follow.

Lastly and importantly, enjoy the journey into the depths of TypeScript!

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