How to get multiple values ​​selected in checkbox in js

<input type="checkbox" name="test" value="1" />
<span>
    1
</span>
<input type="checkbox" name="test" value="2" />
<span>
    2
</span>
<input type="checkbox" name="test" value="3" />
<span>
    3
</span>
<input type="checkbox" name="test" value="4" />
<span>
    4
</span>
<input type="checkbox" name="test" value="5" />
<span>
    5
</span>
<input type=&#39;button&#39; value=&#39;提交&#39; onclick="show()" />

function show(){
    obj = document.getElementsByName("test");
    check_val = [];
    for(k in obj){
        if(obj[k].checked)
            check_val.push(obj[k].value);
    }
    alert(check_val);
}