What is the html lost focus event?

HTML is a very commonly used language in web development. It can build the structure and content of web pages. However, in actual development, it is often necessary to monitor behavioral changes of HTML elements, such as focus events. HTML lost focus event is an event triggered when the user removes focus from the current element. This article will introduce what the HTML lost focus event is and how to use it in web development.

1. What is HTML lost focus event

HTML lost focus event refers to an event triggered when the user removes focus from the current element. In practical applications, focus refers to the element or control that the user is operating, which can be a text box, button, link or other HTML element. After the user types or operates in an element, if they click elsewhere on the page or press the Tab key to move to the next element, the previous element will lose focus and trigger a lost focus event.

HTML lost focus event can be used to verify user-entered data, perform an operation, or clear user-entered content. You can associate a function with the focus loss event by defining the onBlur attribute on the element. For example:

<input>

The above code defines a text box element. When the user removes focus from the element, the checkUsername() function will be executed.

2. Application scenarios of HTML lost focus event

HTML lost focus event can be applied to a variety of scenarios. Here are some common application scenarios:

1. Form verification: When the user inputs data, they can verify whether the format, length, etc. of the data meet the requirements when the input box loses focus.

2. Password matching: When the user enters a password, when the second input box loses focus, it can be checked whether the two entered passwords are consistent.

3. Automatic saving: When the user enters or modifies data, the save operation can be performed when the input box loses focus to ensure that the data will not be lost.

4. Input prompt: When the user inputs content in the input box, Ajax technology can be used to send a request to the server and return the corresponding prompt information when the input box loses focus.

5. Printing function: After the user inputs content in the input box, the printing function can be called when the input box loses focus to implement the printing function.

3. How to use HTML lost focus event

Using HTML lost focus event requires the following steps:

1. Define the onBlur attribute in the HTML element and set it Is the name of a JavaScript function that will be executed when the focus loss event is triggered.
2. Write a JavaScript function to handle the focus loss event. For example, you can validate entered data or perform an action in a function.

The following is an example that demonstrates how to verify the phone number entered by the user when the input box loses focus:

<script>
function checkPhone(phone) {
    var regex = /^1[3|4|5|7|8][0-9]{9}$/; //正则表达式，验证输入的电话号码是否合法
    if (regex.test(phone.value)) {
        alert("电话号码格式正确！");
    } else {
        alert("电话号码格式错误，请重新输入！");
        phone.focus(); //使输入框重新获得焦点
    }
}
</script>


请输入电话号码：<input>

The above code defines an input box element. When the user changes from the input box When the focus is removed, the checkPhone() function will be executed, which is used to verify whether the phone number entered by the user is legal. If the format of the entered phone number is correct, a prompt box will pop up, otherwise the text box will be refocused so that the user can re-enter it.

4. Summary

HTML lost focus event is an event triggered when the user removes focus from the current element. In web development, it has many application scenarios, such as form validation, password matching, automatic saving, etc. Using the HTML lost focus event requires defining the onBlur attribute in the HTML element and writing a JavaScript function to handle it. I hope this article can help readers better apply HTML lost focus events and improve the efficiency and quality of web page development.

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