How to judge whether there is what you want when multiple checkboxes are selected_javascript skills

When I was working on a project today, I encountered a problem. After the checkbox is selected, the selected value will be assigned to a variable. Based on the value of this variable, it is controlled whether a button on the page is displayed.

var temp = ""; 
for(){ 
var bool = ""; 
//给temp赋值 
if(temp == '31'){ 
bool += "false"; 
} 
} 
if(bool.indexOf("false") >= 0){ 
document.getElementById("myid").style.display="none"; 
}else{ 
document.getElementById("myid").style.display="inline"; 
}