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How to use JavaScript to change the input box border after filling it?

王林
王林forward
2023-09-09 19:37:021489browse

如何使用 JavaScript 填充输入框后更改输入框边框？

style.border property is used to change the border of the element. It returns the three border-bottom properties of the element, namely border-color, border-style and border -width. It is one of the HTML style object properties.

We use the onchange event to make changes take effect after filling in the box. onchange is one of the JavaScript attributes that occurs when the value of an HTML element changes. It also works with radio buttons and checkboxes when the selected state changes.

The

onchange event can also be used with

In this article, we will learn how to change the input box border after filling it using JavaScript.

grammar

The following is the syntax of the style.border property, which is used to change the input box border after filling the box -

object.style.border = "width style color|initial|inherit"

parameter

  • width – used to set the border width. We can pass the width value as Thick, Thin, Medium or as a value in px (i.e. 10px).

  • style – used to set the border style. We can pass style values ​​as "solid", "dotted", "double", etc.

  • color – used to set the border color.

  • initial – used to set a property to its default value.

  • inherit – used to inherit properties from parent elements.

return value

Style border returns a string value that represents the color, width, and style of the element's border.

step

After filling the box, we should follow the steps given below to change the input box border -

  • Step 1 - Define the form element with input fields of text and button type.

  • Step 2 - The script code defines the function of changing the border of the input box after filling the box.

  • Step 3 - In the JavaScript section, declare the onchange event, which occurs when the element's value changes.

  • Step 4 - style.border is the HTML DOM background property used to change the bottom border of the element.

  • Step 5 - Whenever the user adds some value to the input value, the onchange event is fired and when that event is fired, the value is checked if it is null. If the value exists and is not empty, the bottom of the border will change to a green dotted line.

Example

In the example below, we use JavaScript to change the filled border of the first input box to "10px solid green" and the second input box border to "3px dotted red". 

<html>
<body style="text-align: center;">
   <h2>Changing the Borders of Input Box after filling the Box</h2>
   <!--defining the form-->
   <form>
      <label>First Name:</label>
      <input type="text" id="firstname" name="firstname" value=""><br><br>
      <label>Second Name:</label>
      <input type="text" id="secondname" name="secondname" value=""><br><br>
      <input type="button" value="submit">
   </form>
   <script>
      var tp = document.getElementById("firstname");
      var tp1 = document.getElementById("secondname");
      tp.onchange = function (f) {
         if (tp.value != '') {
            f.target.style.border = "10px solid green";
         }
      };
      tp1.onchange = function (g) {
         if (tp1.value != '') {
            g.target.style.border = "3px dotted red";
         }
      };
   </script>
</body>
</html>

Example

Only change the lower border of the input box

In this example, we use the style borderBottom property to change the bottom border of the input box. To make changes take effect, we use the onchange event attribute. 

<html>
<body style="text-align: center;">
   <h2>Changing the bottom border of Input Box after filling the box</h2>
   <form>
      <label>First Name:</label>
      <input type="text" id="firstname" name="firstname" value=""><br><br>
      <label>Second Name:</label>
      <input type="text" id="secondname" name="secondname" value=""><br><br>
      <input type="button" value="submit">
   </form>
   <script>
      var tp = document.getElementById("firstname");
      var tp1 = document.getElementById("secondname");
      tp.onchange = function (f) {
         if (tp.value != '') {
            f.target.style.borderBottom = "thick solid #00ff00";
         }
      };
      tp1.onchange = function (g) {
         if (tp1.value != '') {
            g.target.style.borderBottom = "3px dotted green";
         }
      };
   </script>
</body>
</html>

in conclusion

In this article, we demonstrate through examples how to change the border of an input box after filling it. We've seen the tan example where the bottom border changes to green whenever we enter text in both input fields. The color will not change if the value in both input fields is empty, it will only change if the value is present.

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