javascript calls background method c

As a front-end programming language, JavaScript is mainly used for interaction and dynamics of web pages. However, with the development of technology, JavaScript has attracted more and more attention from developers in terms of back-end programming. Especially after the emergence of Node.js, JavaScript has become a full-stack programming language. When developing using JavaScript in the background, calling background methods is an important function. Let's briefly introduce how to call background methods in JavaScript.

1. Use the XMLHttpRequest object to call background methods

The XMLHttpRequest object is an object commonly used in JavaScript to exchange data with the server. It can update the web page without reloading the page.

1.1 Create an object

When creating an XMLHttpRequest object, you can use the following code:

var xhr = new XMLHttpRequest();

1.2 Specify the request method and request address

When creating an XMLHttpRequest After the object, you need to specify the request method and the requested address. The request method can be GET or POST, and the request address refers to the URL address of the background method. This is achieved through the following code:

xhr.open('GET', '/backend_method_url', true);

1.3 Send a request

After specifying the request method and request address, send a request to the server through the following code:

xhr.send();

1.4 Set the callback function

After the request is sent, a callback function needs to be set to process the status and data of the request response. This is achieved through the following code:

xhr.onreadystatechange = function () {
    if (xhr.readyState === 4 && xhr.status === 200) {
        var responseText = xhr.responseText;
        console.log(responseText);
    }
}

Among them, xhr.readyState represents the status of the XMLHttpRequest object, and the status values ​​are as follows:

• 0: Not initialized
• 1: Already The open method is called, the send method is not called
• 2: The send method is called, and the request is being sent
• 3: The data returned by the server is being received
• 4: All data is received , you can use the responseText attribute to obtain all response data

xhr.status represents the HTTP status code, the status code value is as follows:

• 200: Request successful
• 404: The requested resource does not exist
• 500: Server error

1.5 Sending data

In addition to obtaining the data of the background method, we are making a request to the background method , you can also send some data. This is achieved through the following code:

xhr.send('user_name=Tom&password=123456');

The parameter of the 'send' method is the data to be sent, which can be in the form of a string or form data. It can be received through parameters in the background method.

2. Use fetch API to call background methods

fetch API is a new network request API that can be used to replace the XMLHttpRequest object. Use the fetch API to conveniently make AJAX requests and process response data.

2.1 Send a request

The way to send a request using the fetch API is as follows:

fetch('/backend_method_url', {
    method: 'GET'
}).then(function (response) {
    return response.text();
}).then(function (data) {
    console.log(data);
});

The first parameter is the URL address of the background method, and the second parameter is the request containing Objects containing information such as methods, request headers, and request bodies.

2.2 Processing responses

In terms of response processing, response data can be processed through the then method. In the first then method, the response data can be converted into text form for easy processing.

The following is a complete example of using the fetch API to send a request:

fetch('/backend_method_url', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json'
    },
    body: JSON.stringify({
        user_name: 'Tom',
        password: '123456'
    })
}).then(function (response) {
    return response.json();
}).then(function (data) {
    console.log(data);
}).catch(function (error) {
    console.log(error);
});

3. Use the jQuery framework to call background methods

jQuery is a commonly used JavaScript library that provides Many optimized features to simplify JavaScript programming. When making AJAX requests, using jQuery can more conveniently complete the processing of requests and responses.

3.1 Send a request

When using jQuery to send a request, you can use the following code to achieve it:

$.ajax({
    url: '/backend_method_url',
    type: 'GET'
}).done(function (data) {
    console.log(data);
}).fail(function (error) {
    console.log(error);
});

The 'url' attribute specifies the URL address of the background method, 'type 'Attribute specifies the request method.

3.2 Sending data

When using jQuery to send data, it can be achieved through the following code:

$.ajax({
    url: '/backend_method_url',
    type: 'POST',
    data: {
        user_name: 'Tom',
        password: '123456'
    }
}).done(function (data) {
    console.log(data);
}).fail(function (error) {
    console.log(error);
});

The 'data' attribute specifies the data to be sent.

The above is how to use JavaScript to call background methods. Since JavaScript interacts with the background in a more common way, the code syntax is simpler, and only a few lines of code are needed to complete regular operations. Of course, there are many details and knowledge points that we need to understand and use when writing background functions. Fortunately, there are many excellent tutorials and cases on the Internet for us to learn and refer to. More and more developers choose to use JavaScript to develop the backend. This is also because JavaScript has many advantages in terms of syntax and features. I hope the above content will be helpful to everyone.

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