<input type="checkbox" name="hoge" value="ほげ" onchange="onChangeGetCheckBox()" />
<input type="checkbox" name="hoge" value="ふが" onchange="onChangeGetCheckBox()" />
<input type="checkbox" name="hoge" value="ぴよ" onchange="onChangeGetCheckBox()" />

function onChangeGetCheckBox() {
    let elems = document.getElementsByName('hoge');
    for (let i = 0; i < elems.length; i++) {
        if (elems[i].checked === true) {
            alert (elems[i].value);
        }
    }
}