javascript - 这个错误的解决办法是什么？

Question

这里我有一个 Javascript 文件 - 我知道代码现在非常困惑，但我只是编写一些基本功能，然后我将清理代码。该页面分为三个部分，这三个单独的部分是图片。图片应该每 30 秒更换一次。是什么导致了这个错误？

打印到控制台的错误:TypeError: undefined is not an object (evaluating 'document.images[1].src = images[alternate]')

代码如下:

var alternate = 0;
var timerId;
var images = ["img/s1.jpg", "img/tourism.jpg", "img/s2.jpg", "img/shopping.jpg", "img/dining.jpg", "img/shopping2.jpg", "img/s3.jpg"]; // Image URLs in a image array

function startAnimation() {

    var now = new Date();
    var hours = now.getHours();
    var minutes = now.getMinutes();
    var seconds = now.getSeconds();
    var meridian = "AM";
    var time = hours + ":" + minutes + ":" + seconds + " " + meridian;

    if (hours < 12 && meridian == "PM" || hours == 0) {
        hours = hours + 12;
        meridian == "AM";
        time = hours + ":" + minutes + ":" + seconds + " " + meridian;
    } else if (hours > 12 && meridian == "AM") {
        meridian = "PM";
        hours = hours - 12;
        time = hours + ":" + minutes + ":" + seconds + " " + meridian;
    }
    //hours < 12 ? meridian : "AM";

    // comment on code here.
    if (minutes < 10) {
        minutes = "0" + minutes;
        time = hours + ":" + minutes + ":" + seconds + " " + meridian;
    }

    // comment on code here.
    if (seconds < 10) {
        seconds = "0" + seconds;
        time = hours + ":" + minutes + ":" + seconds + " " + meridian;
    }

    //alternate = (alternate == 0) ? 1 : 0; // Alternate images

    if (alternate == 0) {
        alternate = 3;
    } else {
        alternate = 0;
    }

    if (alternate == 1) {
        alternate = 2;
    } else {
        alternate = 1;
    }

    //document.images[0].src = images[alternate];  // Update image
    document.images[1].src = images[alternate];
    timerId = setTimeout("startAnimation()", 30000); // 30 second update

    if (images[alternate] == images[0]) {
        console.log(time + " " + images[0] + " has been loaded.");
    }

    if (images[alternate] == images[3]) {
        console.log(time + " " + images[3] + " has been loaded.");
    }

    if (images[alternate] != images[0] || images[alternate] != images[3]) {
        console.log("Please wait while the debugging process is in effect.");
    }

}

 startAnimation();

Answer 1

你的拼写错误和错误很少:

meridian == "AM";

必须是meridian = "AM";

还有

timerId = setTimeout("startAnimation()", 30000);

必须是:

setTimeout(startAnimation, 30000);