DeepSeek vs Gemini vs Mistral: TypeScript

Prompt
typescript 5.5 guide
DeepSeekDeepSeek
typescript 5.5 guide

Of course! TypeScript 5.5, released in June 2024, is a feature-packed update that brings significant performance improvements, new type predicates, and several other enhancements that make JavaScript development safer and more efficient.

Here is a comprehensive guide to the key features and changes in TypeScript 5.5.

1. The inferred Keyword in Template String Types

This is a powerful new feature for type-level string manipulation. It allows you to "capture" parts of a string template literal type during inference.

The Problem Before:
Previously, extracting parts of a string was cumbersome and often required complex recursive conditional types.

// Old way: Using a complex conditional type
type ExtractName<T> = T extends `Hello, ${infer Name}` ? Name : never;
type OldName = ExtractName<"Hello, Alice">; // type OldName = "Alice"

The New Way with inferred:

The new inferred syntax is more intuitive and declarative. It feels like destructuring at the type level.

// New way: Using the `inferred` keyword directly in the template
type NewName<T> = T extends `Hello, ${inferred Name}` ? Name : never;
type Name = NewName<"Hello, Alice">; // type Name = "Alice"

You can capture multiple parts at once:

type SplitAtUnderscore<S> = S extends `${infer First}_${infer Rest}` ? [First, Rest] : [S];
type Parts = SplitAtUnderscore<"foo_bar">; // type Parts = ["foo", "bar"]

Why it's better: It's syntactically cleaner and makes complex string parsing types much easier to write and read.

2. Regular Expression Syntax Checking

TypeScript can now validate your regular expression patterns at compile time! If you provide a string that is not a valid regex to APIs like RegExp constructor, TypeScript will give you an error.

// This is a valid regex
const validRegex = new RegExp("[a-z]+"); // OK
// This is NOT a valid regex! TypeScript 5.5 will catch this.
const invalidRegex = new RegExp("[a-z"); 
// Error: "Unterminated character class."

Why it's better: Catches a common class of bugs earlier, right in your editor, without having to run your code.

3. Isolated Declarations

This is a major feature for library authors and large monorepos. --isolatedDeclarations allows declaration files (.d.ts) to be generated in parallel, significantly speeding up build times.

What it does: It enables a build process where multiple .ts files can have their .d.ts declaration files generated simultaneously by different processes (e.g., using tsc --declaration --emitDeclarationOnly in a parallelized build tool).

How to use it: Add the flag to your tsconfig.json.

{
  "compilerOptions": {
    "declaration": true,
    "isolatedDeclarations": true
  }
}

Why it's better: Dramatically faster build times for projects that generate declaration files, especially in CI/CD pipelines.

4. Performance and Optimizations

TypeScript 5.5 includes massive performance gains in several key areas:

  • Faster Incremental Builds (--build): The --build mode (used with project references) now avoids saving state to disk that is unnecessary for the next build, leading to 2-3x faster incremental build times in many scenarios.

  • --watch Mode: The --watch mode has been rewritten to be more responsive and use less CPU.

  • --isolatedDeclarations: As mentioned above, this enables parallelization, which is a huge performance win.

  • Memory Usage: Reduced memory usage for object types, leading to faster type-checking and lower overall memory footprint.


5. Preserved Narrowing in Closures Following Last Assignments

TypeScript's control flow analysis has been improved to preserve narrowed types in closures, if the variable is not reassigned after the closure is created.

function validateInput(input: string | number) {
  if (typeof input === "string") {
    // input is narrowed to 'string' here
    setTimeout(() => {
      // In TypeScript 5.4 and earlier, `input` would revert to `string | number` here.
      // In TypeScript 5.5, it correctly remains 'string'.
      console.log(input.toUpperCase()); // OK!
    });
  }
}

Why it's better: More intuitive and correct type narrowing in asynchronous and callback-heavy code.

6. ECMAScript Set Methods

TypeScript now includes type definitions for the new ECMAScript Set methods, which are useful for mathematical set operations.

const firstSet = new Set([1, 2, 3]);
const secondSet = new Set([2, 3, 4]);
// Union: all elements from both sets
const union = firstSet.union(secondSet); // Set<1, 2, 3, 4>
// Intersection: elements present in both sets
const intersection = firstSet.intersection(secondSet); // Set<2, 3>
// Difference: elements in first set but not in second
const difference = firstSet.difference(secondSet); // Set<1>
// Symmetric Difference: elements in either set but not in both
const symmetricDifference = firstSet.symmetricDifference(secondSet); // Set<1, 4>
// Check if one set is a subset of another
const isSubset = firstSet.isSubsetOf(secondSet); // false

Why it's better: Provides type-safe access to these useful utility methods on Set objects.

7. Other Notable Changes


  • Array.prototype.flatMap is No Longer readonly: The return type of flatMap is now writable, aligning with the actual ECMAScript spec behavior.

  • Type Inference for Array.from: Improved inference when using Array.from with a mapFn argument.

  • Experimental Support for get and set Accessors in Object.groupBy: Type definitions for this new JavaScript feature.


How to Get Started


  • Install via npm:

npm install -D typescript@latest

or
npx tsc --init # to create a new tsconfig.json with the latest settings

  • Update your tsconfig.json: Ensure your target is at least "ES2024" to get the full benefit of new lib definitions (like the Set methods).

{
      "compilerOptions": {
        "target": "ES2024",
        "lib": ["ES2024", "DOM", "DOM.Iterable"],
        "module": "ESNext",
        // ... other options
      }
    }

Summary

TypeScript 5.5 is a robust release focused on:

  • Developer Experience: New inferred syntax and regex validation.

  • Performance: Massive build speed improvements.

  • Correctness: Better control flow analysis and updated lib definitions.


It's a highly recommended upgrade for all TypeScript projects. For the complete list of changes, always refer to the official TypeScript 5.5 release notes.

19:43
GeminiGoogle
typescript 5.5 guide

Alright, let's break down TypeScript 5.5. This release isn't a massive overhaul, but it introduces some solid improvements and features.

Key Features and Changes

  • Type Narrowing Improvements:

  • Exhaustive switch Narrowing for Union Type enums: TypeScript can now reliably check for completeness in switch statements when dealing with enums within union types. This eliminates the need for defensive programming in these cases.


enum Status {
            Open,
            Closed,
            InProgress
        }
        type Item =
            | { type: "task"; status: Status }
            | { type: "bug"; status: Status };
        function processItem(item: Item) {
            switch (item.type) {
                case "task":
                    switch (item.status) {
                        case Status.Open:
                            console.log("Task is open");
                            break;
                        case Status.Closed:
                            console.log("Task is closed");
                            break;
                        case Status.InProgress:
                            console.log("Task is in progress");
                            break;
                        // TypeScript now correctly infers that all possible values of Status are covered
                        // No need for `default:` or `assertNever(item.status)`
                    }
                    break;
                case "bug":
                    switch (item.status) {
                        case Status.Open:
                            console.log("Bug is open");
                            break;
                        case Status.Closed:
                            console.log("Bug is closed");
                            break;
                        case Status.InProgress:
                            console.log("Bug is in progress");
                            break;
                    }
                    break;
            }
        }

  • Symbol Discriminants in Union Types: You can now use Symbol properties as discriminants in union types. This is useful when you want to ensure type safety with unique identifiers that are not easily accessible or predictable.


const kindA = Symbol();
        const kindB = Symbol();
        type A = { kind: typeof kindA; value: string };
        type B = { kind: typeof kindB; value: number };
        type Union = A | B;
        function process(union: Union) {
            if (union.kind === kindA) {
                console.log(union.value.toUpperCase()); // TypeScript knows it's type A
            } else {
                console.log(union.value + 10); // TypeScript knows it's type B
            }
        }
        const a: A = { kind: kindA, value: "hello" };
        const b: B = { kind: kindB, value: 42 };
        process(a); // Prints HELLO
        process(b); // Prints 52

  • using Declarations:

  • Resource Management with using: This is a new experimental feature (enabled with --experimentalDecorators and --target esnext or later) that provides automatic resource management using the using keyword. It ensures that resources are disposed of when they go out of scope, much like using in C# or try...finally in JavaScript, but with a cleaner syntax.


interface Disposable {
            [Symbol.dispose](): void;
        }
        class File implements Disposable {
            private fileHandle: number; // Pretend this is a real file handle
            constructor(filename: string) {
                this.fileHandle = this.openFile(filename); // Simulated file opening
                console.log(`File ${filename} opened`);
            }
            private openFile(filename: string): number {
                // Simulate opening a file
                console.log(`Simulating opening file ${filename}`);
                return Math.random(); // Return a placeholder file handle
            }
            read(): string {
                // Simulate reading from the file
                return "Some data from the file.";
            }
            [Symbol.dispose]() {
                this.closeFile(this.fileHandle);
                console.log("File disposed");
            }
            private closeFile(handle: number) {
                // Simulate closing a file
                console.log(`Simulating closing file with handle ${handle}`);
            }
        }
        function processFile(filename: string) {
            using file = new File(filename);  // File is disposed when exiting this scope
            console.log(file.read());
        }
        processFile("myFile.txt");
        // Output:
        // Simulating opening file myFile.txt
        // File myFile.txt opened
        // Some data from the file.
        // Simulating closing file with handle [some random number]
        // File disposed

  • Async Resource Management with await using: For asynchronous resource disposal, use await using with objects that implement Symbol.asyncDispose.


interface AsyncDisposable {
            [Symbol.asyncDispose](): Promise<void>;
        }
        class AsyncFile implements AsyncDisposable {
            private fileHandle: number;
            constructor(filename: string) {
                this.fileHandle = this.openFile(filename);
                console.log(`AsyncFile ${filename} opened`);
            }
            private openFile(filename: string): number {
                console.log(`Simulating opening async file ${filename}`);
                return Math.random();
            }
            async read(): Promise<string> {
                return "Some async data.";
            }
            async [Symbol.asyncDispose](): Promise<void> {
                await this.closeFile(this.fileHandle);
                console.log("AsyncFile disposed");
            }
            private async closeFile(handle: number): Promise<void> {
                await new Promise(resolve => setTimeout(resolve, 50));  // Simulate an async operation
                console.log(`Simulating closing async file with handle ${handle}`);
            }
        }
        async function processAsyncFile(filename: string) {
            await using file = new AsyncFile(filename);
            console.log(await file.read());
        }
        processAsyncFile("asyncFile.txt");
        //Output:
        // Simulating opening async file asyncFile.txt
        // AsyncFile asyncFile.txt opened
        // Some async data.
        // Simulating closing async file with handle [some random number]
        // AsyncFile disposed

  • Why Use using? It's a significant improvement over manually managing resources with try...finally blocks, making code cleaner and less error-prone. It's especially valuable in environments like Node.js where managing file handles, database connections, and other system resources is critical.

  • Inlay Hints for Parameter Names:

  • TypeScript now provides inlay hints for parameter names in function calls. This makes code more readable, especially when function calls have multiple arguments of the same type.

  • Requires editor support (VS Code, for example, has settings to enable this).


function createUser(name: string, age: number, isAdmin: boolean) {
          // ...
        }
        createUser("Alice", 30, true); // Without inlay hints: unclear what each argument represents
        createUser(/*name:*/ "Alice", /*age:*/ 30, /*isAdmin:*/ true); // With inlay hints: clearer

  • Breaking Changes and Considerations:

  • lib.d.ts Changes: There might be minor breaking changes in the standard library definitions (lib.d.ts). Review your code if you're relying on specific, less common parts of the standard library.

  • Compiler Options and Node.js Versions: Ensure your compiler options (tsconfig.json) are compatible with the Node.js version you're targeting. Use the appropriate target and module settings.


How to Upgrade:
  • Install the new version:


npm install -D typescript@latest
    # or
    yarn add -D typescript@latest
    # or
    pnpm add -D typescript@latest

  • Update your VS Code settings (if applicable):

  • Make sure VS Code is using the workspace version of TypeScript (check the TypeScript version in the bottom-right corner). You might need to select "Select TypeScript Version..." from the command palette and choose the version in your node_modules.

  • Update your tsconfig.json:

  • Consider updating the target and module settings to match your desired environment (e.g., esnext or es2022).

  • If you're using the using declarations, add --experimentalDecorators and ensure your target is at least esnext.

  • Test Thoroughly: After upgrading, run your tests to catch any potential compatibility issues. Pay close attention to type errors and runtime behavior.


Example tsconfig.json (with experimental features):

{
  "compilerOptions": {
    "target": "esnext",
    "module": "esnext",
    "moduleResolution": "node",
    "jsx": "react-jsx",
    "esModuleInterop": true,
    "strict": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "experimentalDecorators": true,
    "lib": ["esnext", "dom"] // Include DOM types for browser environments
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

In Summary:

TypeScript 5.5 is a good incremental update focusing on improved type narrowing and experimental resource management. The using declarations, while experimental, have the potential to greatly simplify resource handling in TypeScript/JavaScript projects. Remember to thoroughly test your code after upgrading, especially if you're using experimental features or relying on less common parts of the standard library. Also enable inlay hints to benefit from the code readability improvements.

19:43
MistralMistral AI
typescript 5.5 guide

As of my knowledge cutoff in October 2023, TypeScript 5.5 has not been released, so I can't provide a specific guide for it. However, I can give you a general overview of what you might expect from a new TypeScript release and how to get started with TypeScript in general.

General Overview of TypeScript Releases

TypeScript releases typically include new features, improvements, and bug fixes. Here are some common areas where you might see updates:

  • Language Features: New syntax or constructs that make the language more expressive or easier to use.

  • Type System Improvements: Enhancements to the type system to make it more powerful and flexible.

  • Tooling: Improvements to the TypeScript compiler (tsc), language server, and other tools.

  • Performance: Optimizations to make the compiler faster and more efficient.

  • Compatibility: Ensuring compatibility with the latest JavaScript features and standards.


Getting Started with TypeScript

If you're new to TypeScript, here's a basic guide to get you started:

1. Installation

First, you need to install TypeScript. You can do this using npm (Node Package Manager):

npm install -g typescript

2. Setting Up a Project

Create a new directory for your project and navigate into it:

mkdir my-typescript-project
cd my-typescript-project

Initialize a new npm project:

npm init -y

Install TypeScript locally to your project:

npm install typescript --save-dev

3. Configuration

Create a tsconfig.json file to configure your TypeScript project:

npx tsc --init

This will generate a tsconfig.json file with default settings. You can customize this file to suit your project's needs.

4. Writing TypeScript Code

Create a new TypeScript file, for example, index.ts:

// index.ts
function greet(name: string): string {
    return `Hello, ${name}!`;
}
console.log(greet("World"));

5. Compiling TypeScript

Compile your TypeScript code to JavaScript using the TypeScript compiler:

npx tsc

This will generate a index.js file in your project directory.

6. Running the Compiled Code

You can run the compiled JavaScript code using Node.js:

node index.js

Key Features to Look Out For

While I can't provide specifics for TypeScript 5.5, here are some features that have been introduced in recent versions that you might find useful:

  • Control Flow Analysis: Improvements in how TypeScript analyzes control flow to provide better type inferences.

  • Template Literal Types: Allows for more expressive type manipulations using template literals.

  • Variadic Tuple Types: Enhances the ability to work with tuples of varying lengths.

  • Module Augmentation: Improvements in how you can extend existing modules.

  • Project References: Better support for large projects with multiple sub-projects.


Staying Updated

To stay updated with the latest TypeScript releases and features, you can follow the official TypeScript blog and GitHub repository:


Conclusion

While I can't provide a specific guide for TypeScript 5.5, this overview should help you get started with TypeScript and understand what to look for in new releases. Always refer to the official documentation and release notes for the most accurate and up-to-date information.

19:43

💡 Try this comparison yourself:Compare AI models side-by-side on SNEOS

Analysis

This comparison demonstrates the different approaches each AI model takes when responding to the same prompt. Here are the key differences observed:

Response Characteristics

DeepSeek: Provides a direct response with 88 sentences.

Gemini: Provides a direct response with 122 sentences.

Mistral: Provides a direct response with 45 sentences.

Key Takeaways

  • Each model brings unique strengths to this type of query
  • Response styles vary significantly between models
  • Consider your specific use case when choosing between these models

Try This Comparison Yourself

Want to test these models with your own prompts? Visit SNEOS.com to compare AI responses side-by-side in real-time.

This comparison was generated using the SNEOS AI Comparison ToolPublished: October 01, 2025 | Models: DeepSeek, Gemini, Mistral