How to handle asynchronous code with Promises in TypeScript



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Handling asynchronous code with Promises in TypeScript is a common task, and TypeScript provides strong support for working with Promises. Here's a basic guide on how to handle asynchronous code with Promises in TypeScript:

  1. Defining a Promise: Start by defining a function that returns a Promise. The Promise constructor takes a function with two arguments: resolve and reject.

    typescript
    function asyncFunction(): Promise<string> {
    return new Promise((resolve, reject) => {
        // Asynchronous code here
        // If successful, call resolve with the result
        // If there's an error, call reject with the error
    });
}

  2. Using async/await: TypeScript allows you to use async and await to write asynchronous code in a more synchronous-looking manner. Use the async keyword with a function that contains asynchronous operations, and then use await to wait for the promise to resolve.

    typescript
    async function doAsyncOperation(): Promise<void> {
    try {
        const result = await asyncFunction();
        console.log(result);
    } catch (error) {
        console.error(error);
    }
}

doAsyncOperation();

  3. Handling Promise Results: When dealing with promises, you can use .then() and .catch() to handle the resolved value or the rejection.

    typescript
    asyncFunction()
    .then(result => {
        console.log(result);
    })
    .catch(error => {
        console.error(error);
    });

  4. Promise Chaining: You can chain multiple promises using .then().

    typescript
    asyncFunction()
    .then(result => {
        return anotherAsyncFunction(result);
    })
    .then(finalResult => {
        console.log(finalResult);
    })
    .catch(error => {
        console.error(error);
    });

  5. Type Safety with Generics: If your asynchronous function returns a specific type, use generics to enforce type safety.

    typescript
    function asyncFunction<T>(): Promise<T> {
    return new Promise((resolve, reject) => {
        // Asynchronous code here
    });
}

asyncFunction<string>()
    .then(result => {
        console.log(result);
    })
    .catch(error => {
        console.error(error);
    });

Remember that TypeScript helps catch potential errors at compile-time, providing better type safety when working with Promises. Ensure that your TypeScript configuration has the --strict flag enabled for maximum type safety.

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