当用户尝试减去时，如果没有更多要减去的东西，则提醒用户

Question

我有一个有两个按钮的页面：

• One将1个单位的物品添加到用户的库存中。
• One从用户的库存中删除该物品的1个单位。在这个例子中，这个东西将是钻石。

每次用户拿起或丢下钻石时，都会有一条消息告诉他总共有多少钻石。

我不希望这些消息过于泛泛，比如：“你有1个菱形(S)”。

我设法生成了不同的消息，这取决于用户拥有的菱形数量，以及他是在拿起它们，还是在丢弃它们：

我也希望有自定义的消息，当用户试图拾起一个钻石时，他的钱包已经满了，当他试图丢弃一个时，他没有任何钻石下降。例如：

“你不能再摘钻石了，你的钱包已经满了。”和“你没有任何钻石可丢弃。”

这就是我需要帮助的地方。

正如您将在下面的代码中看到的，我让diamondCount == 0在函数中放置菱形，以生成消息"You drop your last菱形“。如果用户试图从这一点放入另一个菱形，diamondCount仍将为0。那么，当用户刚刚到达0，以及当他试图从0开始丢弃菱形时，我如何区分它呢？

这就是我所拥有的：

​

        function pickDiamond() {
            if (typeof(Storage) !== "undefined") {
                if (localStorage.diamondCount < 10) {
                    localStorage.diamondCount = Number(localStorage.diamondCount) + 1;
                } else {
                    localStorage.diamondCount = 10;
                }
                if (localStorage.diamondCount == 1) {
                    document.getElementById("result").innerHTML = "You picked up your first Diamond!";
                } else {
                    document.getElementById("result").innerHTML = "You picked up a Diamond. You now have a total of " + localStorage.diamondCount + " Diamonds in your wallet.";
                }
            }
        }

        function dropDiamond() {
            if (typeof(Storage) !== "undefined") {
                if (localStorage.diamondCount > 0) {
                    localStorage.diamondCount = Number(localStorage.diamondCount) - 1;
                } else {
                    localStorage.diamondCount = 0;
                }
                if (localStorage.diamondCount == 1) {
                    document.getElementById("result").innerHTML = "You dropped 1 Diamond. You only have 1 Diamond left in your wallet.";
                } else if (localStorage.diamondCount == 0) {
                    document.getElementById("result").innerHTML = "You dropped your last Diamond. You don't have any Diamonds now.";
                } else {
                    document.getElementById("result").innerHTML = "You dropped a Diamond. You now have a total of " + localStorage.diamondCount + " Diamonds in your wallet.";
                }
            }
        }

        function dropAllDiamonds() {
            localStorage.diamondCount = 0;
            document.getElementById("result").innerHTML = "You dropped all your Diamonds.";
        }

    <p>Use the buttons to pick up or drop Diamonds</p>
    <p><button onclick="pickDiamond()" type="button">Pick up Diamonds</button></p>
    <p><button onclick="dropDiamond()" type="button">Drop Diamonds</button></p>
    <p><button onclick="dropAllDiamonds()" type="button">Drop All Diamonds</button></p>
    <p id="result"></p>

​

Answer 1

看起来你的问题是if/else逻辑的问题之一。具体地说，你应该能够用一个if/else链做任何你想做的事情。我对你的代码做了一些修改，如下所示：

对于pickDiamond，我从钻石计数为零开始，并随着用户库存的增加在逻辑序列中添加新的文本。只处理数字，增量运算符在这里比较合适。一旦用户的库存达到10，逻辑将默认为“您不能再摘钻石了。您的钱包已经满了。”最后的else语句。为了测试，我创建了一个localStorage对象。

    let localStorage = {
        diamondCount: 0
    }
    function pickDiamond() {
        if (typeof(Storage) !== "undefined") {
            if (localStorage.diamondCount == 0) {
                localStorage.diamondCount++;
                document.getElementById("result").innerHTML = "You picked up your first Diamond!";
            } else if (localStorage.diamondCount < 10) {
                localStorage.diamondCount++;
                document.getElementById("result").innerHTML = "You picked up a Diamond. You now have a total of " + localStorage.diamondCount + " Diamonds in your wallet.";
            } else {
                document.getElementById("result").innerHTML = "You cannot pick any more diamonds. Your wallet is already full.";
            }

            }
        }

类似的解决方案也可以用于dropDiamond函数，但反之亦然。dropAllDiamonds函数不需要改动就能正常工作。

        function dropDiamond() {
        if (typeof(Storage) !== "undefined") {
            if (localStorage.diamondCount > 2) {
                localStorage.diamondCount--;
                document.getElementById("result").innerHTML = "You dropped a Diamond. You now have a total of " + localStorage.diamondCount + " Diamonds in your wallet.";                 
            } else  if (localStorage.diamondCount == 2) {
                localStorage.diamondCount--;
                document.getElementById("result").innerHTML = "You dropped 1 Diamond. You only have 1 Diamond left in your wallet.";                    
            } else if (localStorage.diamondCount == 1) {
                localStorage.diamondCount--;
                document.getElementById("result").innerHTML = "You dropped your last Diamond. You don't have any Diamonds now.";
            } else {
                document.getElementById("result").innerHTML = "You don't have any Diamonds to drop ya dingus";
            }
        }
    }
        function dropAllDiamonds() {
             localStorage.diamondCount = 0;
             document.getElementById("result").innerHTML = "You dropped all your Diamonds.";
    }