Java腳本：加減變量連續使用的onclick按鈕

Question

我要不斷地通過連續點擊按鈕添加數字：

function burgersub(){ 
    if(document.getElementById("burg").value - 1 < 0) 
    return; 
    else 
     document.getElementById("burg").value--; 
} 
function burgeradd(){ 
    document.getElementById("burg").value++; 
} 

現在這裏是按鈕的形式我的HTML代碼：

<p><button class="btn btn-default" onclick="burgeradd()">+</button><button class="btn btn-default" onclick="burgersub()">-</button></p> 
<input readonly="yes" type="text" class="form-control" id="burg" placeholder="Amount"> 

Answer 1

<script type="text/javascript"> 
function burgersub(){ 
    if(document.getElementById("burg").value - 1 < 0) 
    return; 
    else 
     document.getElementById("burg").value--; 
} 
function burgeradd(){ 
    var quantity = document.getElementById("quantity").value++; 
    quantity++; 
    var price = document.getElementById("price").value; 
    alert(quantity); 
    if (price) { 
     document.getElementById("burg").value = price * quantity; 
    } 
} 
</script> 
p><button class="btn btn-default" onclick="burgeradd()">+</button><button class="btn btn-default" onclick="burgersub()">-</button></p> 
<input readonly="yes" class="form-control" id="quantity" placeholder="Quantity"> 
<input readonly="yes" class="form-control" id="burg" placeholder="Amount"> 
<input class="form-control" id="price" placeholder="Price"> 

新增2個文本框來設定價格，看數量和價格

Answer 2

假設（從OP的評論），你想添加一個固定數量的頂部的項目數量：

var burgers = 0; 
var cost = 1; 
var counter = document.getElementById("burg"); 

function burgersub(){ 
    burgers = Math.max(0, --burgers); 
    counter.value = burgers * cost; 
} 

function burgeradd(){ 
    burgers += 1; 
    counter.value = burgers * cost; 
}