Jquery Wait for Function to Return Before Continue
JavaScript wait for function to finish can be understood as a command that helps to solve the problem of synchronous behavior JavaScript may impose.
When we refer to "the typical synchronous behavior of JavaScript", we are talking about the fact that the previous code has finished before a function is executed in this programming language.
To make it even simpler for you, the JavaScript wait function works like this: the prior function is completed, and only then is the next part of the code executed!
Very useful, right? The only way to learn more about JavaScript wait for function to finish, is by continuing to read this article!
Contents
- JavaScript Wait for Function to End: Is JavaScript Asynchronous or Not?
- – How Does Wait for Function to End Work?: An Example
- – How the Example Applies to Asynchronous Code
- – JavaScript is a Lazy Language: Code Example
- – Notes on the Code Sample
- – Javascript is Synchronous, After All: What To Do About It
- Waiting Until the Function Is Done in JavaScript Using Callback Functions
- – Callback Function Example in Code
- – Executing Two Functions One After The Other
- – Callback Scenario Using the setTimeout Function
- – Final Thoughts on the Callback Pattern
- JavaScript Wait for Function to Return: The Promise Approach
- – JavaScript Promise Forms
- – Benefit of Promise Approach
- – Final Thoughts on the Promise Pattern
- Making Asynchronous Programming Easier With Async and Await
- – The Async Keyword
- – The Await Keyword
- – Async Function-Based Promises: Use the "Await" Function
- – Promise-Based Function: A Code Example
- Conclusion
JavaScript Wait for Function to End: Is JavaScript Asynchronous or Not?
Asynchronous programming is a system where long-running actions (such as web requests) are performed in a separate thread. As a result, the main execution is not stopped while the long-running action is occurring.
The results of the javascript wait until function is done are made available when the main program is notified, and after the function is done, it can actually use those results.
– How Does Wait for Function to End Work?: An Example
To help you visualize this, imagine yourself as though you are carrying a stack of heavy chairs. Holding all of them in your arms makes it virtually impossible to do anything else, let alone help someone do another task
When the code is being executed, it is unable to assist with other tasks. Other codes cannot be executed since the code is now preventing it from happening.
Simply put, you cannot stop a function in JavaScript from executing so that another function can be performed instead. The current command in JavaScript wait until the function completes before another command is executed.
Let us revisit the previous case. If you wanted just to add one chair, what would happen?
You may feel disheartened when you think about going back to where you initially selected the seats and get another chair on top of the stack you already have in your hands. It would be quite difficult and annoying having to let go of the chairs and picking them back up after you have stacked another chair in there.
The answer? Let someone you trust – family or a close friend – do the job.
– How the Example Applies to Asynchronous Code
Asynchronous code is kind of like this. In JavaScript, a task is delegated to another component, which takes care of it. Then the program gets back to what it was doing before. If you use JavaScript wait until function completes, there will be feedback on the results.
– JavaScript is a Lazy Language: Code Example
Now that we know JavaScript is lazy, you should realize that it's also is not willing to do the labor that a few tasks require. Thus, it passes it on to someone else.
For example, if you write a JavaScript code as:
console.log("1st");
}
function second() {
console.log("2nd");
}
function third() {
console.log("3rd");
}
first();
second();
third();
When JavaScript executes your code, it will do it from top to bottom, which means the result will be as seen as:
The code in this step will add a call to the first() function to the delay process, which can be corrected by using the setTimeout() method, like here:
first();
}, 0);
second();
third();
The result would be as follows:
– Notes on the Code Sample
The code sample above demonstrates how to utilize the setTimeout() function. While in a traditional web application, you could substitute the setTimeout() method with a call to the fetch() function, in a real-world online application, it is more efficient to do this by using the get() function.
JavaScript will not wait for fetch() to respond by running the code below it.
console.log(response); // undefined
– Javascript is Synchronous, After All: What To Do About It
Since JavaScript is a synchronous programming language, there are multiple approaches that will make your work easier, which would allow functions to be executed in the way and order you want htem to.
The approaches that alter the JavaScript wait until function include:
- Callbacks
- Promises
- Async/Await Keywords
Waiting Until the Function Is Done in JavaScript Using Callback Functions
A callback function is a function commonly used in JavaScript. The callback function will later be called by the accepting function. The function that receives a callback function is free to call anytime during its function execution. It's very common to see a callback function get called right at the end of the receiving function's execution.
By utilizing the callback pattern, you may provide the next function to call as a callback to the preceding function. Additionally, you have to tell the function that will receive a callback that it should invoke the specified function at the appropriate time.
The callback pattern enables you to delay running the following piece of code until the previous operation is finished.
– Callback Function Example in Code
We know it all might sound a little bit complicated, but the JavaScript example code below will help:
console.log("One");
}
function Two(){
console.log("Two");
}
one();
Two();
Output:
– Executing Two Functions One After The Other
Now if you want to execute the two functions, in a way that functionOne() should be executed after executing functionTwo() your code should be structured like this:
// do some asynchronous work
_callback();
}
function functionTwo(){
// do some asynchronous work
functionOne(()=>{
console.log("I am a callback");
});
}
functionTwo();
– Callback Scenario Using the setTimeout Function
The final item displayed in the console after running the above code is "I am a callback." The well-known callback use scenario may be described as the setTimeout function, with a handler function as the function to run after clocking out. Here is what it would look like with the setTimeout function:
console.log("log before use setTimeout function");
setTimeout(()=>{
console.log("inside timeout");
},5000);
console.log("log after use setTimeout function");
}
testCallBack();
Output:
log after use setTimeout function
inside timeout
– Final Thoughts on the Callback Pattern
Furthermore, the callback pattern is not intuitive and is prone to cause callback hell where the next piece of code is nested inside the previous one.
The more complex your code is, the harder it will be to understand and tweak your code. That's why you should resort to the callback pattern only when you run out of other options.
JavaScript Wait for Function to Return: The Promise Approach
A promise is a JavaScript object that represents an uncertain future value. In the final analysis, a promise is nothing more than telling the program what it should do something – the value – in the future. JavaScript wait for function to return value can be achieved with the promise approach. In the above situation, it is possible that the information is derived via an API call, or it might be an error object from a failed network request.
Whatever it is, you might need to use one of the JavaScript forms of a promise. Let's take a look at what these are.
– JavaScript Promise Forms
A JavaScript promise may be in one of these states:
- fulfilled – The action has been performed successfully.
- rejected – no action was performed because it failed
- pending – The action has not been performed yet.
- settled – the action has been accepted or refused
To decide whether to act or not, a promise gets resolved and a reject function. These functions are given the task of triggering one of these states.
– Benefit of Promise Approach
The main benefit of the promise approach is that you can connect functions that you want to happen when the outcome is successful (resolve) or when the outcome is unsuccessful (reject).
Let's look at these two functions alongside some other important ones you need to know if you want to make use of the promise approach:
- Resolve() is similar to then(), while reject() is like catch()
- To register a function to execute successfully, we use a period (.) and then (.then).
- We register a function to execute when a process fails by using a period (.) and catch (.catch)
– Final Thoughts on the Promise Pattern
Furthermore, The promise pattern enables you to progressively call your functions by calling the next function within the then() method. Also, you could create consecutive callbacks while avoiding the callback pattern using the promise pattern.
If you want to go through with the consecutive callbacks, you don't need to do anything with a fetch() request when it's fulfilled. As fetch() fulfils promises, you may chain it with then() and catch() methods to handle it and create the callbacks without using the pattern.
Finally, let's move on to learn about the keywords async and await, which are part of the Promise-based paradigm.
Making Asynchronous Programming Easier With Async and Await
Async functions and the await keyword were introduced in ECMAScript 2017, so they are a relatively new addition to the JavaScript programming world.
There are two parts to using async/await in your code.
– The Async Keyword
Basically, the async keyword is used to turn functions asynchronous. An async function is a function that is able to anticipate that the await keyword may be used to execute asynchronous code.
– The Await Keyword
The only time you'll start to appreciate the benefit of an async function is when you add the await keyword. Normally, the "await" function should only be used together with the async functions in conventional JavaScript code. However, it may be used alone when using JavaScript modules.
– Async Function-Based Promises: Use the "Await" Function
For async function-based promises, you may add the "await" function to stop the function in javascript, until the promise is fulfilled, and then return the result value.
As a general rule, await should be used anytime you're calling any function that returns a Promise.
– Promise-Based Function: A Code Example
Here is an example of a promise-based function:
return new Promise((resolve,reject)=>{
//here our function should be implemented
setTimeout(()=>{
console.log("Hello from inside the testAsync function");
resolve();
;} , 5000
);
});
}
async function callerFun(){
console.log("Caller");
await testAsync();
console.log("After waiting");
}
callerFun();
Output:
Hello from inside the testAsync function
After waiting
Conclusion
By now, you should have all the information you need with regards to JavaScript wait for function to finish. In a gist, here is what we covered in this article:
-
JavaScript is lazy and single-threaded. - This lazy attitude of JavaScript means that one function has to run before another can be executed.
- To resolve this issue, you can use the callback approach, promise approach, or the Async and the await keyword.
- The promise approach and the async/await keywords work better than the callback approach.
Knowing the different approaches mentioned will come in handy to you, and you are free to choose whichever one works best for the type of program you want to create. We are more than sure that our suggestions on how to use the JavaScript wait for function to end will prove to be helpful for you!
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