Proficient in Javascript Reading Notes 1

Javascript proficiency

Chap 1

1. Use a namespace to protect your database.

YAHOO.util.Event.addListner(...);

Chap 2

2. Reference

Multiple variables can point to the same object. A reference can only point to a specific object, rather than another reference. Multi-layer references are not allowed.

However, when the string connection operation is executed, the result is always a New String object instead of the modified version of the source string.

Eg1.

var object=new Object();var objRef=obj;obj.oneProperty=true;alert(obj.oneProperty === objRef.oneProperty);

Eg2.

var items=new Array("one","two","three");var itemsRef=items;items=new Array("new","Array");alert(items!=itemsRef);

Eg3.

var item="test";var itemRef=item;item+="ing";alert(item!=itemRef);

 

3. Determine the input parameter type

If no parameter is provided, the type must be undefined.

if( typeof msg == 'undefined') {...}

1) typeof statement

This is a good solution when the variable is not of the object or array type. However, for a custom object, for example, a user cannot use this method for type check, because it only returns the object.

2) constructor

This property references the function originally used to construct the object.

// check numberif(num.constructor == String)      num=parseInt(num); //check arrayif(str.constructor == Array)      str=str.join(',');

3) Comparison between typeof and constructor

Variable	Typeof variable	Constructor
{An: "object "}	Object	Object
["An", "array"]	Object	Array
Function (){}	Function	Function
"A string"	String	String
55	Number	Number
True	Boolean	Boolean
New User ()	Object	User