How to use JavaScript to implement the automatic verification function when the email input box loses focus

With the rapid development of the Internet, email has become an indispensable part of people's daily life and work. There are also more and more usage scenarios for email, such as social networking, work, business, etc. For websites and applications, email verification has also become an essential link. This article will introduce how to use JavaScript to implement the automatic verification function when the email input box loses focus.

First of all, we need to clarify what the email format is and what kind of string is the email address. The common email format consists of a username and a domain name, connected with the "@" symbol. For example, a complete email address might be example@domain.com. If the string we enter conforms to this format, then we can consider it to be a valid email address.

Next, we implement the function of losing focus verification email through JavaScript code.

The first step is to get the value in the input box. Get the value in the email input box through getElementById or other selector methods.

var emailInput = document.getElementById("email");
var email = emailInput.value;

The second step is to verify the email format. In JavaScript, you can use regular expressions to verify whether a string conforms to a specific format. For email verification, we can use the following regular expression:

var emailPattern = /^[^\.][\w.-]+@\w+(\.\w+)+\w$/;

This regular expression means that first the string cannot start with a dot, and then accepts letters, numbers, underscores, dots and dashes, @ The symbol must be followed by a paragraph of English letters, and dots and English letters are accepted. The last \w is the terminator, make sure the ends are all English letters or numbers.

Then we use this regular expression to verify whether the email entered by the user meets the format requirements.

if (emailPattern.test(email)) {
  // 邮箱格式正确
} else {
  // 邮箱格式错误
}

The third step is to feed back the verification results to the user. We can dynamically change the color and content of the input box border and prompt information based on the verification results.

if (emailPattern.test(email)) {
   emailInput.style.borderColor = "";
   emailInput.style.backgroundColor = "";
   emailHint.innerHTML = "";
} else {
   emailInput.style.borderColor = "red";
   emailInput.style.backgroundColor = "#FFE3E3";
   emailHint.innerHTML = "邮箱格式不正确！请重新输入。";
}

In this code snippet, when the email format is correct, we set the border color and background color of the input box to empty, and the prompt information is cleared; when the email format is incorrect, we set the border color of the input box Set it to red, set the background color to light pink, and prompt the user with an error message.

The last step is to bind the verification results with the process of submitting the form. We can implement automatic verification by listening to the onblur event of the email input box.

emailInput.onblur = function() {
   // 验证邮箱格式
}

This will automatically call the verification function when the user removes focus after entering their email address.

Through the above steps, we can use JavaScript to implement the automatic verification function when the email input box loses focus.

Overall, JavaScript lost focus verification email is a very useful feature. It can effectively prevent users from submitting invalid email addresses when filling out forms, and can improve the efficiency and experience of users filling out forms. For website and application developers, understanding how this feature is implemented can allow them to better develop more stable and user-friendly websites and applications.

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