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Working process- Various functions are added to the stack during the execution of a code. Later, the functions are executed one by one. The function that appears at the top of the stack is executed before the others. So, push and pop are the two primary operations performed on the stack.
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The async await js is of great use to the company as it loads the application and screen faster to provide the best user experience.
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The Blocking technique makes it difficult for the users to execute the code. This is because it delays the execution time making it an impossible task to overcome the processing issues.
Here’s a code snippet for the same.
The callback is just an event handler used to execute the requests stored in the memory. The callback is a function passed as an argument to another function. Callback functions are executed automatically with respect to the pending requests. Callbacks are the main source through which the asynchronous functions implement.
Knowing the fact that the setTimeout method executes only after the given amount of time, the other method executes by then. It has two arguments- callback and the time(in milliseconds).
Now, we will take an example of a callback function.
In the above example, the second function is executed before waiting for the first function. However, waiting for a function is a concept used by the callback function.
The output for this function is given below.
The code was executed synchronously. Here, sayName() function is used as an argument in the greet() function.
Also, check ut the blog – Node.js Process
Event handlers are a form of asynchronous programming language that helps you to call a specific function when an event occurs. The users are then notified about the calling function.
The XMLHttpRequest API is used to create http requests to a server. This process takes up a lot of time and hence is known as an asynchronous API, that notifies the user about the progress of a request. This progress is shared using the event listeners that are attached together with the object of the XMLHttpRequests.
Let us look at it with an example. We will use a click to start the request handler. Here, we will first create an XMLHttpRequest and then we will capture the event.
Once, the code is executed, you will get a message saying “Finished!”. This is where the execution ends.
Once we add the event listener, the user gets a request.
There are 3 common ways to assign event handlers to a specific request. We will discuss each of them briefly.
The most common event handler names begin with on. The event handler for a click event is known as a click. To attach the event handler along with an HTML element, you can use the event handler attribute. Here’s how you can use this event handler.
While assigning the event handler, you need to avoid using special characters such as &, “ “, <, etc.
The script function in the handler can be written as follows-
Every element has an event handler attribute named onclick. You just need to assign the values to a specific function. Here’s how you can do this.
In the above code, the function acts as a button element. You can even access the properties within the event handling function. The Dom Level 0 event handler is most widely used because of its browser support and its simplicity level.
The DOM level 2 Event handler is the other form of event handling technique. It provides two methods to deal with the event listeners. They are- addEvenetListener and removeEventListener. The former is used to register a specific event. While the latter is used to remove that particular event.
Let us discuss both of them in detail.
This method takes 3 arguments- event handler, event name, and a boolean value. This value is used to call the event handler when it has a true value. You can add more than 1 event handler to a single event.
As the name suggests, the removeEventListener removes an event that was added using the addEventListener method.
The event handling loop finds the status of the stack used within the heap memory. When the stack gets empty, it calls out for the remaining requests. While we handle the events, the queue contains only a few pending requests. Hence, the callback shifts at the top of the stack and executes the remaining queries.
In synchronous js, one code is executed at a time. The other codes are kept on hold for a while. The next one is unblocked as soon as the previous execution takes place.
In asynchronous js, you can execute more than 1 code at a time without waiting for the results.
Asynchronous JS is a concept that allows the users to run their time-taking codes and still respond to other tasks as well. The users no longer need to wait for the execution of extended programs. They can compiler other codes while waiting for a response.
Async js is used to perform long network requests simultaneously. It does not block the main thread execution. Instead, it runs them parallelly.