What are the six data types in javascript? js data types and common implicit conversion logic (introduction)

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1. Six data types

Primitive type (basic type): access by value, The actual value stored in the variable can be manipulated. Null and undefined are special among primitive type summaries.

Reference type: The value of a reference type is an object stored in memory.

* Unlike other languages, JavaScript does not allow direct access to locations in memory, which means that the memory space of an object cannot be directly manipulated. When you manipulate an object, you are actually manipulating a reference to the object rather than the actual object. So values ​​of reference types are accessed by reference.

2. Implicit conversion

1. And-

Smart use of the and-rules Conversion type

Convert the variable into a number: num-0;

Convert the variable into a string: num '';

2, a==b

Same type, same as ===

Different type, try type conversion and comparison:

3, a===b

is of different types, return false

is of the same type:

##3. Packaging objects

4. Type detection

• typeof

• instanceof

• Object.prototype.toString

• constructor

• duck type

1, typeof

2. instanceof

instanceof is very useful when determining whether an object is an array, Data, regular expression, etc.

Instanceof Pit: Instanceof cannot be used for object type detection between different windows or iframes!

3. Object.prototype.toString

It should be noted that Object.prototype.toString in IE6/7/8. apply(null) returns "[object Object]".

4. Constructor

Any object has a constructor attribute. If it is inherited from the prototype, the constructor will point to the constructor that constructs the object. device or constructor.

The constructor can be overridden, so use it with care.

5. duck type

For example, if you don’t know whether an object is an array, you can determine whether its length is a number and whether it has arrays such as join and push. Methods. Determining whether an object belongs to certain types through some characteristics is sometimes used.

Summary:

##6. How to detect that a variable is a string

var str="hello";
var temp=str+'';
temp===str
//tru

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