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JavaScript prohibits input

王林

Release： 2023-05-12 10:16:06

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JavaScript Input Forbidden

With the continuous development of the Internet, JavaScript has become an indispensable part of modern web design. JavaScript can enhance the interactivity of web pages and make it easier for users to enter and operate data. However, in some cases, we need to implement some functions that restrict user input through JavaScript. For example, prohibit users from entering specific characters or limit the number of characters that users can enter, etc. This article will help you implement these functions by explaining some JavaScript techniques.

Prohibit the input of specific characters

If you want to prohibit the input of certain characters in the user input box, you can use JavaScript regular expressions to achieve this. For example, if you want the user to only enter numbers, you can use the following code in the onkeypress event of the user input box:

function checkNumber(event) {
  var charCode = event.keyCode;
  if (charCode < 48 || charCode > 57) {
    event.preventDefault();
  }
}

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In this code, we first obtain the ASCII code of the characters entered by the user, Then determine whether the character is a number. If not a number, the event.preventDefault() method is called to prevent the default character input event.

Similarly, if you want to prevent users from entering other specific characters, just modify the judgment conditions. For example, if you want to prevent users from entering letters and punctuation marks, you can use the following code:

function checkCharacter(event) {
  var charCode = event.keyCode;
  if ((charCode >= 65 && charCode <= 90) || (charCode >= 97 && charCode <= 122) || (charCode >= 33 && charCode <= 47) || (charCode >= 58 && charCode <= 64) || (charCode >= 91 && charCode <= 96) || (charCode >= 123 && charCode <= 126)) {
    event.preventDefault();
  }
}

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In this code, we modify the judgment condition to judge whether the characters are letters or punctuation marks.

No spaces allowed

Sometimes, we hope that users cannot enter spaces when entering data. This can be achieved by detecting whether the characters entered by the user are spaces. For example, you can use the following code in the onkeypress event of the user input box:

function checkWhiteSpace(event) {
  var charCode = event.keyCode;
  if (charCode === 32) {
    event.preventDefault();
  }
}

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In this code, we determine whether the characters entered by the user are spaces, and if so, call the event.preventDefault() method. Prevents the default character input event.

Prohibit input exceeding the specified number of characters

If you want to limit the number of characters the user enters in the input box, you can do this by detecting the number of characters in the user input box. For example, you can use the following code in the oninput event of the user input box:

function limitInput(event, maxLength) {
  var input = event.target.value;
  if (input.length > maxLength) {
    event.target.value = input.slice(0, maxLength);
  }
}

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In this code, we first get the value in the user input box and determine whether the number of characters exceeds the specified maximum Number of characters (maxLength). If it exceeds, the first maxLength characters are intercepted and written back to the input box.

Complete example

The following is a complete example, which demonstrates how to use JavaScript to implement functions such as prohibiting the input of specific characters, prohibiting the entry of spaces, and prohibiting the entry of more than a specified number of characters:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>JavaScript 禁止输入</title>
</head>
<body>
  <form>
    <label>只能输入数字：</label>
    <input type="text" onkeypress="checkNumber(event)">
    <br><br>
    <label>不能输入空格：</label>
    <input type="text" onkeypress="checkWhiteSpace(event)">
    <br><br>
    <label>最多只能输入 5 个字符：</label>
    <input type="text" oninput="limitInput(event, 5)">
  </form>

  <script>
    function checkNumber(event) {
      var charCode = event.keyCode;
      if (charCode < 48 || charCode > 57) {
        event.preventDefault();
      }
    }

    function checkWhiteSpace(event) {
      var charCode = event.keyCode;
      if (charCode === 32) {
        event.preventDefault();
      }
    }

    function limitInput(event, maxLength) {
      var input = event.target.value;
      if (input.length > maxLength) {
        event.target.value = input.slice(0, maxLength);
      }
    }
  </script>
</body>
</html>

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In this example, we created a form with three input boxes, which are used to demonstrate the functions of prohibiting the entry of numbers, prohibiting the entry of spaces, and prohibiting the entry of more than a specified number of characters. Each input box is bound to a corresponding JavaScript event handler.

Conclusion

By using JavaScript, we can easily implement various functions that restrict user input. This not only improves the security and data quality of the website, but also provides users with a better interactive experience. We hope this article helps you better use JavaScript to implement your web design.

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