Javascript array problem: Cannot read property 'src' of undefined_问答_开发者

Javascript array problem: Cannot read property 'src' of undefined

开发者 https://www.devze.com 2023-03-31 20:49 出处：网络

This script has been running over at waterbirds.org for years. Now it\'s broken for开发者_C百科 some reason. It throws a \"Cannot read property \'src\' of undefined\" error and I\'ve tracked it down t

This script has been running over at waterbirds.org for years. Now it's broken for开发者_C百科 some reason. It throws a "Cannot read property 'src' of undefined" error and I've tracked it down to preLoad[j].src (first line of runSlideShow function) as the problem because I can put a image link address there and it works. Any idea what's causing the problem?

// Waterbird Society Theme for Wordpress
// Rotating image banner applet
//
// Usage:
//<body onLoad='rotate_banner(slideShowSpeed, "Image1.jpg", "Image2.jpg"...)'>



var slideShowSpeed;
var j = 0;
var p;
var preLoad = new Array();

function rotate_banner() {
    var args = rotate_banner.arguments;
    slideShowSpeed = Number(args[0]);
    p = args.length;
    for (i = 0; i < p-1; i++) {
        preLoad[i] = new Image();
        preLoad[i].src = args[i+1];
    }
    runSlideShow();
}

function runSlideShow() {
    document.images['SlideShow'].src = preLoad[j].src;
    j++;

    if (j > (preLoad.length - 1)) j = 0;

    t = setTimeout('runSlideShow()', slideShowSpeed*1000);
}

Everything is alright with your code except for it is run globally so all var declarations create global variables.

The exact issue on waterbirds.org is that j variable is defined somewhere before and by the moment it comes to preLoad[j] j equals 96, and preload[96] is really undefined.

Wrap your banner in anonymous self-executing function, for example, to make vars local, and you're done:

(function(){

var slideShowSpeed;
var j = 0;
var p;
var preLoad = new Array();

// to keep rotate_banner global, save it as a property of window object
window.rotate_banner = function() {
    var args = rotate_banner.arguments;
    slideShowSpeed = Number(args[0]);
    p = args.length;
    for (i = 0; i < p-1; i++) {
        preLoad[i] = new Image();
        preLoad[i].src = args[i+1];
    }
    runSlideShow();
}

function runSlideShow() {
    document.images['SlideShow'].src = preLoad[j].src;
    j++;

    if (j > (preLoad.length - 1)) j = 0;

    t = setTimeout('runSlideShow()', slideShowSpeed*1000);
}

})()

And remember: global variables are evil! =)