When you use await, the module that called it pauses execution until the awaited promise resolves. Sibling modules continue to execute in a synchronous order as long as there are no cycles of awaited promises in the graph. Read more about : await is only valid in async functions and the top level bodies of modules.
What is SyntaxError: await is only valid in async functions?
If you see a SyntaxError error, it is a good idea to evaluate your programming environment to make sure that you are both seeing the same error. This is because some errors are more difficult to spot than others. For example, if you are using Jupyter Notebooks to program, you may find it harder to spot indentation errors because the editor will replace spaces with tabs.
Another thing to consider is the location of the error in your code. There are three different types of errors: syntax, runtime, and logical errors. Runtime errors are errors that are triggered when the program is being executed. Examples of this include attempting to divide by zero or passing an invalid argument to a function.
Logical errors are errors that occur in the logic of the code and can be very difficult to identify. Examples of logical errors are failing to properly capitalize a word, trying to insert an item into a container that is not empty, or using an integer that is too large for a typecasting operation.
Logical errors are often very difficult to debug, as they can occur at any stage of the compilation and execution process. Because of this, they should be avoided whenever possible. Fortunately, there are some tools that can help you detect logical errors in your code, such as TypeScript Checker and Flow Charts. These tools can help you find errors before they are triggered at runtime, so that your application will not crash. These tools can also help you analyze the cause of the error so that you can fix it.
Why SyntaxError: await is only valid in async functions?
The await expression is used in async functions to pause the execution of the function until the promise it is waiting on is fulfilled or rejected. The wait operation unwraps the underlying promise and returns the fulfillment value, or if the promise is not thenable, the expression’s own value. It also throws the rejection reason if the promise is rejected.
The async/await pair is a syntactic sugar for writing asynchronous code that looks synchronous, but it has some limitations and performance penalties. It is important to understand how the await operator works in order to write asynchronous code that is safe and performant.
Asynchronous code is a series of asynchronous operations that are nested inside one another. Each asynchronous operation returns a promise. The async/await pair helps simplify asynchronous code by enabling you to create promises that are chained together using the then() method. This helps you to write cleaner asynchronous code and provides a more synchronous experience for the caller of your asynchronous function.
When you use the await keyword, you must make sure that it is only used in async functions or in the top level bodies of modules. Otherwise, you will receive the syntax error SyntaxError: await is only valid in async functions. This error is caused by the fact that await is only valid in async function, and using it outside of these functions will cause a runtime error.
In the example below, the asynchronous function is named fetchUserOrder(). The return type of this function is FutureString>. The async function has an await expression before it calls the asynchronous function createOrderMessage(). The await expression enables the asynchronous fetchUserOrder() to be called in a synchronized way with the asynchronous async function createOrderMessage(). The asynchronous createOrderMessage() will wait for the promise returned by the asynchronous fetchUserOrder(). The asynchronous fetchUserOrder() will then execute.
If you use the await statement outside of async functions or in the top levels of module bodies, then you will receive a runtime error SyntaxError: await is not permitted in this context. The problem is that top-level await halts the execution of all modules in the module graph until the current module’s awaited promise is resolved or rejected. This can lead to deadlock, especially in modules with cyclical dynamic imports.
Prior to the introduction of top-level await, the order in which modules executed was synchronized and deterministic. Top-level await allows modules to declare that they are dependent on other modules, and then wait for those dependencies to complete their top-level await statements before executing their own body.
This guarantee is important to maintain developer expectations that such modules should always be able to execute in a synchronous manner. Read more about : await is only valid in async functions and the top level bodies of modules.
How to Fix SyntaxError: await is only valid in async functions
SyntaxErrors are errors in the syntax of a program that usually occur due to mistakes such as missed reserved keywords, spaces, quotes placed improperly, incorrect usage of blocks, invalid declarations, and missing functions and arguments. These errors can be fixed by checking the code carefully to ensure that it is correctly written.
If you encounter a SyntaxError, you will need to resolve the issue in order to continue writing your program. The first step is to understand the error and how it occurs. Then, you will need to find the source of the error and fix it. Once you have fixed the error, you will be able to continue writing your program without a SyntaxError.
The async and await keywords allow you to write asynchronous code in a cleaner, more readable manner. However, there are some things to keep in mind when using these keywords. For example, the await keyword is only valid in async functions and the top level bodies of modules. It is not valid in synchronous functions or within the body of a lock statement.
An async function is a method, lambda expression, or anonymous function that is marked with the async keyword. The async keyword is used to indicate that the function will return a promise and is executed asynchronously. The await keyword is used to pause the evaluation of the async function until the promise is either resolved or rejected.
If a promise is passed to an await expression, it will wait for the promise to be fulfilled and then return the fulfilled value. This is because async functions are asynchronous and will not block the main thread. Read more about : await is only valid in async functions and the top level bodies of modules.
The await expression in async functions pauses the evaluation of the function and then defers execution of the code that actually depends on the result to a microtask queue. The queue will execute the code after the await expression as soon as it becomes available. This means that you will not have to wait for a long time for your application to complete.
The async and await keywords enable you to write asynchronous code that looks a lot like synchronous code. In addition, the await keyword also enables you to handle errors in a more robust way than traditional synchronous code.
For example, if an asynchronous function such as fetchUserOrder fails, you can catch the failure in a try block and pass the failed promise to the await expression, which will convert the rejection into a caught error.