Discuss why JS needs to be serialized before submitting the form

Javascript is a programming language widely used in web front-ends. In web development, form submission is a very common operation, and in Javascript, form data usually needs to be serialized before submitting the form. This article aims to explore why Javascript needs to be serialized before submitting a form, and how serialization is implemented.

1. Why you need to serialize form data

In HTML, forms are a basic way to collect user input information. When the user clicks the submit button, the form is automatically submitted to the backend server for processing. In Javascript, we often need to submit form data asynchronously through AJAX technology to avoid page jumps. Before submitting the form data, the form data needs to be serialized into a string format and then sent to the backend server for processing through AJAX technology.

So why do you need to serialize form data? This is because when the form is submitted, the browser will automatically encode the data in the form and replace special characters and spaces with URL encoding format. For example, spaces will be converted into " ". The URL encoding format is safe during transmission, but decoding is required during background server processing to obtain the original data. Therefore, in order to avoid the backend server not being able to decode the data correctly, we need to serialize the form data and convert it into a string format before submitting it.

2. Serialization methods of form data

In Javascript, form data can be serialized in the following two ways.

1. Using the FormData object

FormData is a newly introduced data type in HTML5. It can convert form data into a formData object, making it easy to use AJAX technology to asynchronously upload files or submit form data in Javascript. The advantage of using the FormData object to serialize form data is that it supports uploading multiple files at the same time.

The specific implementation method is as follows:

const form = document.querySelector('#myForm');
const formData = new FormData(form);

After constructing the form data into a formData object, you can use AJAX technology to asynchronously submit the form data.

2. Write your own serialization function

Since the FormData object does not support browsers of IE 9 and below, we need to write some code ourselves to implement the sequence of form data. change. The following is a function that can serialize form data into string format:

function serialize(form) {
    let data = '';
    for(let i = 0; i < form.elements.length; i++) {
        let field = form.elements[i];
        if(field.type !== 'checkbox' && field.type !== 'radio' || field.checked) {
            data += encodeURIComponent(field.name) + '=' + encodeURIComponent(field.value) + '&';
        }
    }
    return data.slice(0, -1);
}

This function receives a form as a parameter, and then serializes its data into string format by traversing the form elements.

3. Conclusion

In Javascript, serializing a form is an important step before submitting form data. Serializing the form can avoid the problem that the backend server cannot correctly decode the data, and at the same time, it can easily use AJAX technology for asynchronous submission and processing. For browsers that do not support FormData objects, we can write our own serialization function to serialize form data.

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