'Enhance the robustness of js program code' I see a lot of sample code_javascript skills

In the process of writing and using js programs, we often encounter various errors. For a language that depends on the browser, it is difficult for us to completely control its correct operation at any time. But we still need to make our own efforts to enhance the robustness and security of the js program code we write and reduce the probability of errors as much as possible.
The following are some of my thoughts on enhancing the robustness of js programs that I have summarized in the process of learning js. If you think it is of some value to you, then I have achieved my goal. If you think it is meaningless, Please don't throw bricks, thank you.
(1) It is necessary to determine whether the necessary parameters are passed in correctly.
Code example:

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(2) Different processing is performed according to the type of parameters passed in:

For example, when we want to obtain an html element object, we need to determine whether the passed in is an id or an element object.
Code example:

<title> </title> new document <meta name="generator" content="editplus"> <meta name="author" content=""> <meta name="keywords" content=""> <meta name="description" content=""> <div id="a"> </div>area a<div id="b"> </div>area b
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(3) Set default values ​​for parameters.

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(4) Check the type of parameters passed in.

For example:

We require that a parameter passed in must be a number. Sample code:

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For another example, we may need to pass Parameter sets a width or height value: Sample code:

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(5) In JS OO programming, if the program wants to obtain the current instance name, it must make a judgment on the incoming instance name.
Sample code:

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(6)在解析xml数据之前首先要检查传入xml数据类型（Dom？xml字符串？文件名）及其结构的合法性。
示例代码：

<script language="JavaScript" type="text/javascript"> <!-- function loadXML(xml){ if(window.ActiveXObject){ var xmlDom=new ActiveXObject("Microsoft.XMLDOM"); }else{ if(document.implementation&&document.implementation.createDocument){ var xmlDom=document.implementation.createDocument("","doc",null); } } xmlDom.async=false; xmlDom.preserveWhiteSpace=true; //先作为xml文件加载，再作为xml字串加载 if(!xmlDom.load(xml)){ try{ xmlDom.loadXML(xml); }catch(e){ //非IE浏览器 var oParser=new DOMParser(); xmlDom=oParser.parseFromString(xml,"text/xml"); } } return xmlDom; } function parseXML(xml){ if(!xml){ alert('请设定xml数据'); return ; } var xmlDom=typeof (xml)=="object"?xml:loadXML(xml); //判断是对象还是字符串（字符串包括xml数据串或文件名） if(!xmlDom.documentElement){ alert("提示：非法的xml数据！"); return ; } alert("合法的xml数据！"); } var xmlDom=loadXML("<t><c>dom"); parseXML(); //未设定数据 parseXML("<d><t>test"); //传入合法的xml数据 parseXML("<d><t>"); //传入非法的xml数据 parseXML(xmlDom); //传入Dom类型数据 //parseXML("data.xml") //传入xml文件 //--> </script>
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(7)善用try...catch语句，很多时候的错误我们无法屏蔽，使用try...catch可以很容易的将这些错误过滤掉。
比如当我们在使用userData时，很多浏览器不支持，使用try...catch可以简化我们的处理。

<script language="JavaScript" type="text/javascript"> <!-- try{ //userData操作对象 dataContainer=document.documentElement; dataContainer.addBehavior("#default#userdata"); alert('可以操作userData数据'); }catch(e){ alert('不支持userData,请执行其他操作'); } //--> </script>
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欢迎大家多评论，提出更好更多的建议。
arg==undefined 改成 arg === undefined 可能会好些
var arg1=arg1||"default arg1";
这样写略有点问题
arg1是null 0 "" false都不行

<script language="JavaScript" type="text/javascript"> <!-- alert(null==undefined); alert(null===undefined); //--> </script>
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三个等号表示类型也相等。JS在比较时不会自动转换类型。