JSFiddle - React, Tailwind, and code Playground

HTML

请打开 console 以后再 选择， 按住 Ctrl 或 Shift 多选。<br/>
<select id="select" multiple name="select">
  <option value="value1">Value 1</option> 
  <option value="value2" selected>Value 2</option>
  <option value="value3">Value 3</option>
</select>
<div style="height:50px;"/>

JavaScript

var selectElem = document.getElementById('select');

selectElem.addEventListener('change', onSelect_change);

function onSelect_change(e){
	// get the selected value :
	var selectedValue = e.target[e.target.selectedIndex].value;
  // you can also do it using domEvent.target.value but the other solution allows you to get every option's property you want 
	
	console.log("Selected: " + selectedValue);
  
  const options  = e.target.options;
  
  	console.log("options: " + options);
    console.log(options);

		const area = Object.keys(options)
		.filter(i => options[i].selected === true)
		.map(i => options[i].value);
	
  console.info("area:"+area);
  
}