Javascript 如何根据用户输入和下拉列表查找 html 文件

document.addEventListener('DOMContentLoaded', function(){
    let form   = document.getElementById('search-form');
    let folder = form.querySelector('[name="folder"]');
    let file   = form.querySelector('[name="file"]');

    form.addEventListener('submit', event => {
        event.preventDefault();

        let folderValue = folder.value.trim();
        let fileValue   = file.value.trim();

        if( folderValue && fileValue ){
             window.location = folderValue+'/'+fileValue+".html" 
        }else{
            file.focus();
        }
    })
})

<form id="search-form">
    <select name="folder">
        <option j-link="" value="" selected>please choose folder</option>
        <option j-link="./1/" value="folder1">folder1</option>
        <option j-link="./2/" value="folder2">folder2</option>
        <option j-link="./3/" value="folder3">folder3</option>
    </select>

    <input type="text" name="file" autofocus>
    <button type="submit">Submit</button>
</form>