JavaScript modifies request value

JavaScript is one of the most powerful programming languages ​​that can easily modify any element on the page. In Web development, Ajax and XMLHttpRequest are two very common technologies, and they are widely used in the development of dynamic websites.

XMLHttpRequest is a browser API represented by an XMLHttpRequest object, which can obtain data from the server asynchronously without refreshing the page.

Let's take a look at how to use JavaScript to modify the value of the XMLHttpRequest request. First, we need to create a request object using XMLHttpRequest. Suppose we want to send a POST request to the server. The requested data should contain a form value named "username". We can write it like this:

let xhr = new XMLHttpRequest();
xhr.open('POST', 'http://example.com', true);
xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
let data = 'username=john';
xhr.send(data);

In this example, we create an XMLHttpRequest object and Use the open() method to specify the transport method and URL. The third parameter true indicates an asynchronous request. Then we use the setRequestHeader() method to set the request header and tell the server that the requested data type is in form format.

Finally, we use the send() method to send the data to the server. In this example, we set a form value called "username" to "john". Now, let's say we need to modify its value before sending the request. We can do this:

let xhr = new XMLHttpRequest();
xhr.open('POST', 'http://example.com', true);
xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
let data = 'username=john';
data = data.replace('john', 'smith');
xhr.send(data);

In this example, we use the replace() method to replace "john" in the data with "smith". Now, when we send the request, the value named "username" in the form data will be "smith".

JavaScript also provides an easier way to modify form data. We can use the FormData object to create a form object, and then use the set() method to set the form value. For example, we can write like this:

let xhr = new XMLHttpRequest();
xhr.open('POST', 'http://example.com', true);
let formData = new FormData();
formData.set('username', 'john');
xhr.setRequestHeader('Content-Type', 'multipart/form-data');
formData.set('username', 'smith');
xhr.send(formData);

In this example, we use the FormData() constructor to create a new FormData object and use the set() method to set the form value named "username" . We then set the request header to multipart/form-data and send the request. Before sending the request, we use the set() method again to modify the form value to "smith". After sending the request, the value named "username" in the form data will be "smith".

When using XMLHttpRequest to send a request, modifying the request value is a very useful skill. It can help us better understand Ajax and XMLHttpRequest, and allow us to better control our request data. Whether using the replace() method or the FormData object, the request value can be easily modified to suit our needs.

The above is the detailed content of JavaScript modifies request value. For more information, please follow other related articles on the PHP Chinese website!