来看一个简易的 Javascript 调试包：jscript.debug.js，包含两个函数，第一个用来遍历对象的各个属性；第二个是一个通用的 Debug 函数（其实 说‘对象'比较‘精确些'，呵呵），用来规定各种错误级别及其各种提示、错误信息的格式化显示，还是《Javascript 实战》上面的经典例子，先看源码：

复制代码 代码如下:
/**
* jscript.debug package
* This package contains utility functions for helping debug JavaScript.
*
*/
/*命名空间*/
if (typeof jscript == 'undefined') {
jscript = function() { }
}
jscript.debug = function() { }

/**
* This simple function is one of the handiest: pass it an object, and it
* will pop an alert() listing all the properties of the object and their
* values.（这个函数用来遍历对象的属性及其相应的值，并显示出来）
*
* @param inObj The object to display properties of.
*/
jscript.debug.enumProps = function(inObj) {

var props = "";
var i;
for (i in inObj) {
props += i + " = " + inObj[i] + "\n";
}
alert(props);

} // End enumProps().

/**
* This is a very simple logger that sends all log messages to a specified
* DIV.（这是一个简单的 debug 日志记录系统）
*/
jscript.debug.DivLogger = function() {

/**
* The following are faux constants that define the various levels a log
* instance can be set to output.（下面的常量用来定义错误级别）
*/
this.LEVEL_TRACE = 1;
this.LEVEL_DEBUG = 2;
this.LEVEL_INFO = 3;
this.LEVEL_WARN = 4;
this.LEVEL_ERROR = 5;
this.LEVEL_FATAL = 6;

/**
* These are the font colors for each logging level.（定义各种错误的显示颜色）
*/
this.LEVEL_TRACE_COLOR = "a0a000";
this.LEVEL_DEBUG_COLOR = "64c864";
this.LEVEL_INFO_COLOR = "000000";
this.LEVEL_WARN_COLOR = "0000ff";
this.LEVEL_ERROR_COLOR = "ff8c00";
this.LEVEL_FATAL_COLOR = "ff0000";

/**
* logLevel determines the minimum message level the instance will show.（需要显示的最小错误级别，默认为 3）
*/
this.logLevel = 3;

/**
* targetDIV is the DIV object to output to.
*/
this.targetDiv = null;

/**
* This function is used to set the minimum level a log instance will show.
*（在这里定义需要显示的最小错误级别）
* @param inLevel One of the level constants. Any message at this level
* or a higher level will be displayed, others will not.
*/
this.setLevel = function(inLevel) {

this.logLevel = inLevel;

} // End setLevel().

/**
* This function is used to set the target DIV that all messages are
* written to. Note that when you call this, the DIV's existing contents
* are cleared out.（设置信息显示的 DIV，调用此函数的时候，原有的信息将被清除）
*
* @param inTargetDiv The DIV object that all messages are written to.
*/
this.setTargetDiv = function(inTargetDiv) {

this.targetDiv = inTargetDiv;
this.targetDiv.innerHTML = "";

} // End setTargetDiv().

/**
* This function is called to determine if a particular message meets or
* exceeds the current level of the log instance and should therefore be
* logged.（此函数用来判定现有的错误级别是否应该被显示）
*
* @param inLevel The level of the message being checked.
*/
this.shouldBeLogged = function(inLevel) {

if (inLevel >= this.logLevel) {
return true;
} else {
return false;
}

} // End shouldBeLogged().

/**
* This function logs messages at TRACE level.
*（格式化显示 TRACE 的错误级别信息，往依此类推）
* @param inMessage The message to log.
*/
this.trace = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_TRACE) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_TRACE_COLOR + ";'>" +
"[TRACE] " + inMessage + "</div>";
}

} // End trace().

/**
* This function logs messages at DEBUG level.
*
* @param inMessage The message to log.
*/
this.debug = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_DEBUG) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_DEBUG_COLOR + ";'>" +
"[DEBUG] " + inMessage + "</div>";
}

} // End debug().

/**
* This function logs messages at INFO level.
*
* @param inMessage The message to log.
*/
this.info = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_INFO) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_INFO_COLOR + ";'>" +
"[INFO] " + inMessage + "</div>";
}

} // End info().

/**
* This function logs messages at WARN level.
*
* @param inMessage The message to log.
*/
this.warn = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_WARN) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_WARN_COLOR + ";'>" +
"[WARN] " + inMessage + "</div>";
}

} // End warn().

/**
* This function logs messages at ERROR level.
*
* @param inMessage The message to log.
*/
this.error = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_ERROR) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_ERROR_COLOR + ";'>" +
"[ERROR] " + inMessage + "</div>";
}

} // End error().

/**
* This function logs messages at FATAL level.
*
* @param inMessage The message to log.
*/
this.fatal = function(inMessage) {

if (this.shouldBeLogged(this.LEVEL_FATAL) && this.targetDiv) {
this.targetDiv.innerHTML +=
"<div style='color:#" + this.LEVEL_FATAL_COLOR + ";'>" +
"[FATAL] " + inMessage + "</div>";
}

} // End fatal().

} // End DivLogger().

源码看完后，我们来测试一下这个“小包”，来看下面的测试源码：

复制代码 代码如下:
<div id="jscript_debug_div" style="font-family:arial; font-size:10pt; font-weight:bold; display:none; background-color:#ffffe0; padding:4px;">

<a href="javascript:void(0);" id="enumPropsLink"
onClick="jscript.debug.enumProps(document.getElementById('enumPropsLink'));">
enumProps()-Shows all the properties of this link(显示此链接标签对象的所有属性和值)
</a>
<br><br>

<div id="divLog" style="font-family:arial; font-size: 12pt; padding: 4px; background-color:#ffffff; border:1px solid #000000; width:50%; height:300px; overflow:scroll;">Log message will appear here</div>
<script>
var log = new jscript.debug.DivLogger();
log.setTargetDiv(document.getElementById("divLog"));
log.setLevel(log.LEVEL_DEBUG);
</script>
<br>
<a href="javascript:void(0);"
onClick="log.trace('Were tracing along now');">
DivLogger.log.trace() - Try to add a TRACE message to the above DIV
(won't work because it's below the specified DEBUG level);
</a><br>
<a href="javascript:void(0);"
onClick="log.debug('Hmm, lets do some debugging');">
DivLogger.log.debug() - Try to add a DEBUG message to the above DIV
</a><br>
<a href="javascript:void(0);"
onClick="log.info('Just for your information');">
DivLogger.log.info() - Add a INFO message to the above DIV
</a><br>
<a href="javascript:void(0);"
onClick="log.warn('Warning! Danger Will Robinson!');">
DivLogger.log.warn() - Add a WARN message to the above DIV
</a><br>
<a href="javascript:void(0);"
onClick="log.error('Dave, there is an error in the AE-35 module');">
DivLogger.log.error() - Add a ERROR message to the above DIV
</a><br>
<a href="javascript:void(0);"
onClick="log.fatal('Game over man, game over!!');">
DivLogger.log.fatal() - Add a FATAL message to the above DIV
</a><br>
<br><br>

</div>

上面的测试代码里面的 <script> 段进行了 debug 的实例化，设置了显示信息的 DIV，而且设置了显示信息的最小级别为：LEVEL_DEBUG：
var log = new jscript.debug.DivLogger();
log.setTargetDiv(document.getElementById("divLog"));
log.setLevel(log.LEVEL_DEBUG);
来看看效果如何呢：
enumProps()-Shows all the properties of this link(显示此链接标签对象的所有属性和值) Log message will appear here DivLogger.log.trace() - Try to add a TRACE message to the above DIV (won't work because it's below the specified DEBUG level); DivLogger.log.debug() - Try to add a DEBUG message to the above DIV DivLogger.log.info() - Add a INFO message to the above DIV DivLogger.log.warn() - Add a WARN message to the above DIV DivLogger.log.error() - Add a ERROR message to the above DIV DivLogger.log.fatal() - Add a FATAL message to the above DIV
[Ctrl+A 全选 注:引入外部Js需再刷新一下页面才能执行]
在点击“enumProps()-Shows all ……”（第一个 link ）的时候浏览器弹出的框如下图所示（Opera），详细地列出了你所点击的 a 标签对象的所有属性及值：