Typescript foreach async await

Introduction

Asynchronous programming can be a little tricky in TypeScript, especially when using the foreach loop. However, with the introduction of async/await, this task has become much easier.

In this tutorial, we will explore how to use foreach loop with async/await in TypeScript.

The problem with foreach loop

In JavaScript/TypeScript, the foreach loop is just a syntax sugar for for loop. However, it has one major drawback – it doesn't wait for the asynchronous operations to complete before moving to the next iteration.

This means that if you are trying to perform some asynchronous operation inside a foreach loop, you might end up with unexpected results. For example, consider the following code:

const asyncFn = async (arg) => {
    // some async operation 
    return result;
}

const someArray = [1,2,3,4,5];

someArray.forEach(async (value) => {
    const result = await asyncFn(value);
    console.log(result);
});

Here, the forEach loop will not wait for each of the asyncFn operations to complete. Instead, it will immediately move to the next iteration, resulting in unexpected output.

The solution - async/await

To solve this problem, we can use async/await syntax. With async/await, we can wait for the asynchronous operation to complete before moving to the next iteration.

Here's how we can use async/await with foreach loop in TypeScript:

const asyncFn = async (arg) => {
    // some async operation 
    return result;
}

const someArray = [1,2,3,4,5];

const asyncForEach = async () => {
    for await (const value of someArray) {
        const result = await asyncFn(value);
        console.log(result);
    }
};

asyncForEach();

Here, we have defined a new asyncForEach function that iterates through the someArray using a for-await-of loop. Inside this loop, we can use await keyword to wait for each asynchronous operation to complete.

Now, when we call asyncForEach function, it will iterate through the someArray, wait for each asyncFn operation to complete, and log the result to the console.

Conclusion

In conclusion, using foreach loop with asynchronous operations in TypeScript can be a little tricky. However, with the help of async/await, we can easily solve this problem and write clean and readable code.

I hope this tutorial was helpful!