Reading "JavaScript advanced Programming" Note one-basic concepts

Grammar

1. Strict mode enables strict mode to add "use strict" above the top of the script or inside the function; Statement.

Data type

2. typeof

   typeof returns a undifined,boolean,number,string,object,function of six strings, typeof null returns "Object".

4. There are six types of data: Undefined,null,boolean,number,string,object
6. Undefined
8. Null

   Although null is equal to undefined, it is used differently. A variable that holds an object is not assigned, and the variable should be saved to null.

10. Boolean

    Data type	The value converted to true	Value converted to False
    Boolean	True	False
    String	Any non-empty string	"" (empty string)
    Number	Any non-0 numeric value (including infinity)	0 and Nan
    Object	Any object	Null
    Undefined	Without any circumstances	Undefined

12. Number

    Octal notation: The number is added in front of 0, and octal is not valid in strict mode.

    Hexadecimal means: 0x before the number.

    Infinity and-infinity represent positive and negative infinity.

    NaN (non-numeric) is not equal to any number.

14. String the

    \ n	line wrapping
    \ t	tabulation
    \b	spaces
    \ r	carriage return
    \f	feed
    \ \	slash
    \ '	single quote
    \ "	double quotes
    \xnn	one character in hexadecimal nn (where n is 0~f). For example \x41 Represents a
    \unnnn	A Unicode character (where n is 0~f) represented in hexadecimal nnnn. For example, \u03a3 means the Greek character σ

    toString () method, which can pass in the cardinality of a parameter, such as binary, num.tostring (2);

    If you do not know if the value to be converted is null or undefined, you can use the string () function, if the value is not null or undefined call the ToString () method, NULL returns "NULL", Undefined returns " Undefined ";

    To convert a value to a string, you can use the  + ""   method;

16. Object

    Common property methods for object instances

    Constructor	Holds the function that is used to create the current object. such as Object ()
    hasOwnProperty (PropertyName)	Used to check whether a given property exists in the current object instance (rather than in the prototype of the instance), PropertyName must be specified as a string. such as O.hasownproperty ("name")
    Ispropertyof (Object)	Used to check if an incoming object is a prototype of another object
    propertyIsEnumerable (PropertyName)	Used to check if the For-in statement can be used to enumerate, PropertyName must be specified as a string.
    Tolocalstring ()	Returns the string object of the object
    ToString ()	Returns the string object of the object
    ValueOf ()	Returns the string, numeric, or Boolean representation of the object, usually the same as the ToString () value

Operator

1. When a unary plus operator is applied to a non-numeric value, the operand converts the value like the number () transformation function.
2. Bitwise non-intrinsic: negative value minus 1 for operand
3. Logic and (&&) operators:

   Returns the second operand if the first is an object

   If the second is an object, the object is returned only if the first operand is true

   Two operands are objects, returns the second operand

   There is an operand that is NULL to return NULL

   There is one operand that Nan returns nan

   There is an operand that is undefined returned undefined

4. Logic or (| |) Operator

   Returns the first operand if the first operand is an object

   Returns the second operand if the evaluation result of the first operand is false

   If two operands are objects, the first operand is returned

   Returns NULL if all two operands are null

   If two operands are Nan, a nan is returned

   If two operands are undefined, the undefined is returned

   Use logic or this behavior to avoid assigning null or undefined values to variables, such as: var myObject = Prrfferredobject | | Backupobject

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Reading "JavaScript advanced Programming" Note one-basic concepts