Query the number of input characters javascript

In recent years, with the rapid development of the Internet, front-end development has received more and more attention. In front-end development, JavaScript is a crucial part. Among them, the function of querying the number of input characters is also a frequently encountered problem. This article will introduce how to use JavaScript to implement the function of querying the number of input characters.

1. Basic knowledge

Before introducing how to implement the function of querying the number of input characters in JavaScript, we need to understand some basic knowledge first. First, we need to know how to get the elements. In JavaScript, we can obtain elements in a variety of ways. Commonly used methods include ID, class, tag name, etc.

Next, we need to understand how to listen for input events. In JavaScript, we can add event listeners to elements through the addEventListener() method. Additionally, we need to know how to get the value entered in the input box. In JavaScript, we can get the value in the input box through the value attribute.

2. Implementation process

After understanding the basic knowledge, we can start to implement the function of querying the number of input characters. The specific implementation process is as follows:

1. Get the input box element and add an event listener

We can get the input box element through the getElementById() method and add an input event listener to it, code As follows:

var input = document.getElementById("input-box"); input.addEventListener("input", function() { // 实现功能代码 });

2. Get the value in the input box

In the input event listener, we can get the value in the input box through the value attribute. The code is as follows:

var inputText = input.value;

3. Calculate the length of the input value and output

With the value in the input box, we can calculate its length. The code is as follows:

var length = inputText.length; console.log("输入字符个数为：" + length);

Finally, combine the above codes and the complete code is as follows:

var input = document.getElementById("input-box"); input.addEventListener("input", function() { var inputText = input.value; var length = inputText.length; console.log("输入字符个数为：" + length); });

3. Notes

When using JavaScript to implement the function of querying the number of input characters When doing this, you need to pay attention to the following points:

1. If you need to display the number of characters on the page, you can insert it into the HTML element through the innerHTML attribute.
2. When getting the value in the input box, you need to note that the newline character will also be counted as one character.
3. When listening for input events, you need to pay attention to compatibility. Lower versions of IE browsers may not support input events. You can consider using onkeyup events or oninput events instead.

4. Summary

Querying the number of input characters is a common function of JavaScript and is often involved in front-end development. This article introduces how to use JavaScript to implement the function of querying the number of input characters, focusing on knowledge points such as obtaining elements, monitoring input events, obtaining the value in the input box, and calculating the character length. I hope this article can be helpful to everyone's front-end development.

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