Question

我正在尝试更换＆＃34; undefined＆＃34;显示已变空的数组时。

这是程序的简化版本，每次按下按钮时，用户都会递减数组。当数组为空时，如果用户继续按下按钮，我希望替换文本＆＃34; undefined。＆＃34;

我玩过＆＃34;而＃34;陈述，以及＆＃34; typeof＆＃34;，但我似乎无法让它发挥作用。

<script>
  basket = ['Apples', 'Bananas', 'Pears'];

  function showFruit() {
    var i = 0; // the index of the current item to show
    fruitDisplay = setInterval(function() {
        document.getElementById('fruit')
            .innerHTML = basket[i++]; // get the item and increment
        if (i == basket.length) i = 0; 
                                   // reset to first element if you've reached the end
    }, 100); //speed to display items

    var endFruitDisplay = setTimeout(function() {
        clearInterval(fruitDisplay);

        var index = basket.indexOf(document.getElementById('fruit').innerHTML);
        basket.splice(index, 1); //remove last shown

    }, 1000); //stop display after x milliseconds

    remain = basket.length;
    document.getElementById("remaining").innerHTML = remain;

    return showFruit;
}

    //if (typeof(basket) == undefined) {
    //fruit = 'Finished';
    //} 

</script>

    <h1><span id = 'fruit'></span> </h1>
    Remaining: <span id="remaining"></span>


 <button onclick="showFruit()">Random Fruit</button>

Answer 1

只测试数组是否为空。

if (basket.length == 0) {
    document.getElementById("fruit").innerHTML = "No fuits left";
} else {
    document.getElementById('fruit')
        .innerHTML = basket[i];
    i = (i + 1) % basket.length // increment with wraparound
}

Answer 2

我看到评论的代码......试试......

if (typeof basket === "undefined") {
  fruit = 'Finished';
}

基本上，这是将typeof与undefined进行比较的正确方法。虽然你的变量typeof不会被定义，所以......

您还可以检查数组长度......

if (basket.length === 0) {
  fruit = 'Finished';
}

替换＆＃34;未定义＆＃34;用文字

2 个答案: