防止 var 变为负值

Question

我有一个带有以 0 开头的 var 的按钮，当您单击另一个按钮时它会增加到 1。但是如果您先单击第二个按钮，则 var 变为负数。该按钮在开始时是禁用的，但是当它增加到 1 时应该启用该按钮。

当页面加载时按钮被禁用，但是当 var 变为 1 时按钮仍然被禁用。我试过了：if(var == 0){document.getElementById("button1").disabled = true; return false;}

Answer 1

您可以像下面的代码片段那样做：

You can use any tag instead of input like div span h1 ... which ever you wish and style according to need .
This thing you will need to change will be change .value to .innerHTML everywhere like this(1 example) :
var units = document.getElementsByClassName("unitsMain")[0].innerHTML

function decreaseUnits() {
  var units = document.getElementsByClassName("unitsMain")[0].value
  if (units > 0) {
    units--;
    document.getElementsByClassName("unitsMain")[0].value = units;
  }
}

function increaseUnits() {
  var units = document.getElementsByClassName("unitsMain")[0].value
  units++;
  document.getElementsByClassName("unitsMain")[0].value = units;
}

<button class="decOrderUnits" onclick="decreaseUnits()"><i class="fa fa-minus"></i>-</button>
<input class="unitsMain" value="0" maxlength="3">
<button class="incOrderUnits" onclick="increaseUnits()"><i class="fa fa-plus"></i>+</button>

防止 var 变为负值

Prevent var from going negative

html

javascript

var

button