JavaScript select Element (ok)

https://www.javascripttutorial.net/javascript-dom/javascript-select-box/

Part 1.

Part 2:

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Select Box</title>
  <link rel="stylesheet" href="selectbox.css">
</head>
<body>
  <div id="container">
    <form>
      <label for="framework">Select one or more JS Frameworks:</label>
      <select id="framework" multiple>
        <option value="1">Angular</option>
        <option value="2">React</option>
        <option value="3">Vue.js</option>
        <option value="4">Ember.js</option>
      </select>
      <button id="btn">Get Selected Frameworks</button>
    </form>
  </div>
  <script>
  const btn = document.querySelector('#btn');
  const sb = document.querySelector('#framework');
  btn.onclick = (e) => {
    e.preventDefault();
    const selectedValues = [].filter
      .call(sb.options, option => option.selected)
      .map(option => option.text);
    alert(selectedValues);
  };
  </script>
</body>
</html>

Summary: in this tutorial, you will learn how to handle the <select> element in JavaScript.

Introduction to the HTML select elements

A <select> element provides you with a list of options. A <select> element allows you to select one or multiple options.

To create a <select> element, you use the <select> and <option> elements. For example:

<select id="framework">
    <option value="1">Angular</option>
    <option value="2">React</option>
    <option value="3">Vue.js</option>
    <option value="4">Ember.js</option>
</select>Code language: HTML, XML (xml)

AngularReactVue.jsEmber.js

The above <select> element allows you to select a single option at a time.

To enable multiple selections, you add multiple attribute to <select> element as follows:

<select id="framework" multiple>
    <option value="1">Angular</option>
    <option value="2">React</option>
    <option value="3">Vue.js</option>
    <option value="4">Ember.js</option>
</select>Code language: HTML, XML (xml)

AngularReactVue.jsEmber.js

The `HTMLSelectElement` type

To interact with <select> element in JavaScript, you use the HTMLSelectElement type.

The HTMLSelectElement type has the following useful properties:

selectedIndex – returns the zero-based index of the selected option. The selectedIndex is -1 if no option is selected. If the <select> element allows multiple selections, the selectedIndex returns the value of the first option.
value – returns the value property of the first selected option element if there is one. Otherwise, it returns an empty string.
multiple – returns true if the <select> element allows multiple selections. It is equivalent to the multiple attribute.

The `selectedIndex` property

To select a <select> element, you use the DOM API like getElementById() or querySelector().

The following example illustrates how to get the index of the selected option:

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript Select Element Demo</title>
    <link href="css/selectbox.css" rel="stylesheet">
</head>
<body>
    <form>
        <label for="framework">Select a JS Framework</label>
        <select id="framework">
            <option value="1">Angular</option>
            <option value="2">React</option>
            <option value="3">Vue.js</option>
            <option value="4">Ember.js</option>
        </select>
        <button id="btn">Get the Selected Index</button>
    </form>
    <script>
        const btn = document.querySelector('#btn');
        const sb = document.querySelector('#framework')
        btn.onclick = (event) => {
            event.preventDefault();
            // show the selected index
            alert(sb.selectedIndex);
        };
    </script>
</body>
</html>Code language: HTML, XML (xml)

How it works:

First, select the <button> and <select> elements using the querySelector() method.
Then, attach a click event listener to the button and show the selected index using the alert() method when the button is clicked.

The `value` property

The value property of the <select> element depends on the <option> element and its HTML multiple attribute:

If no option is selected, the value property of the select box is an empty string.
If an option is selected and has a value attribute, the value property of the select box is the value of the selected option.
If an option is selected and has no value attribute, the value property of the select box is the text of the selected option.
If multiple options are selected, the value property of the select box is derived from the first selected option based on the previous two rules.

See the following example:

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript Selected Value</title>
    <link href="css/selectbox.css" rel="stylesheet">
</head>
<body>
    <div id="container">
        <form>
            <label for="framework">Select a JS Framework:</label>
            <select id="framework">
                <option value="">Angular</option>
                <option value="1">React</option>
                <option value="2">Vue.js</option>
                <option>Ember.js</option>
            </select>
            <button id="btn">Get the Selected Value</button>
        </form>
    </div>
    <script>
        const btn = document.querySelector('#btn');
        const sb = document.querySelector('#framework')
        btn.onclick = (event) => {
            event.preventDefault();
            alert(sb.value);
        };
    </script>
</body>
</html>Code language: HTML, XML (xml)

In this example:

If you select the first option, the value property of the <select> is empty.
If you select the last option, the value property of the select box is Ember.js because the selected option has no value attribute.
If you select the second or third option, the value property will be "1"or "2".

The `HTMLOptionElement` type

In JavaScript, the HTMLOptionElement type represents the <option> element.

The HTMLOptionElement type has the following handy properties:

index – the index of the option inside the collection of options.
selected – returns true when the option is selected. You set this property to true to select an option.
text – returns the option’s text.
value – returns the HTML value attribute.

The <select> element has the options property that allows you to access the collection options:

selectBox.optionsCode language: CSS (css)

For example, to access the text and value of the second option, you use the following:

const text = selectBox.options[1].text;
const value = selectBox.options[1].value;Code language: JavaScript (javascript)

To get the selected option of a <select> element with a single selection, you use the following code:

let selectedOption = selectBox.options[selectBox.selectedIndex];Code language: JavaScript (javascript)

Then you can access the text and value of the selected option via text and value properties:

const selectedText = selectedOption.text;
const selectedValue = selectedOption.value;Code language: JavaScript (javascript)

When a <select> element allows multiple selections, you can use the selected property to determine which options are selected:

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript Select Box</title>
    <link rel="stylesheet" href="css/selectbox.css">
</head>
<body>
    <div id="container">
        <form>
            <label for="framework">Select one or more JS Frameworks:</label>
            <select id="framework" multiple>
                <option value="1">Angular</option>
                <option value="2">React</option>
                <option value="3">Vue.js</option>
                <option value="4">Ember.js</option>
            </select>
            <button id="btn">Get Selected Frameworks</button>
        </form>
    </div>
    <script>
        const btn = document.querySelector('#btn');
        const sb = document.querySelector('#framework');

        btn.onclick = (e) => {
            e.preventDefault();
            const selectedValues = [].filter
                .call(sb.options, option => option.selected)
                .map(option => option.text);
            alert(selectedValues);
        };
    </script>
</body>
</html>Code language: HTML, XML (xml)

In this example, the sb.options is an array-like object, so it doesn’t have the filter() methods like an Array object.

To borrow these methods from the Array object, you use the call() method. For example, the following returns an array of selected options:

[].filter.call(sb.options, option => option.selected)Code language: PHP (php)

And to get the text property of the options, you chain the result of the filter() method with the map() method, like this:

.map(option => option.text);Code language: JavaScript (javascript)

Summary

The <select> element allows you to select one or multiple options. Add the multiple attribute to the <select> element to enable multiple selections.
The HTMLSelectElement represents the <select> element. Use the selectedIndex and value to get the index and value of the selected option.
The HTMLOptionElement represents the <option> element. If the option is selected, the selected property is true. The selectedText and selectedValue properties return the text and value of the selected option.

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Last updated 2 years ago

hashtagPart 1.

hashtagPart 2:

hashtagIntroduction to the HTML select elements

hashtagThe HTMLSelectElement type

hashtagThe selectedIndex property

hashtagThe value property

hashtagThe HTMLOptionElement type

hashtagSummary