JavaScript Data type Casting

First, convert to numeric type

1.number ( parameter ) converts any type to a numeric type

A. if it is a Boolean value,false is 0andtrue is 1

B. if it is a number, the conversion becomes itself. Remove the meaningless back guide 0 .

C. if Null is converted to 0

D. if undefined is converted to NaN not a number

E. if the object calls the object's valueOf () First, if valueOf () returns NaN, then the object is called the toString ()

F. if it is a string

1. If there is only a number in the string, convert to ten ( ignoring leading 0 and 0)

2. if it is a valid canonical floating-point type, convert to a floating-point value ( ignoring leading 0 and trailing 0)

3. if it is an empty string, convert to 0

4. if it is a different value, return NaN

2,parseint ( parameter 1, parameter 2) converts a string to an integer

A. if a string contains only numbers, it is converted to an integer in the form of a binary.

B. he automatically ignores the spaces in front of the string, knowing that the first non-null numeric string is found until the end of the string that resolves to the first non-numeric value.

C.returns NaN If the first character of the string is not a space, number, or-

D. parameter 1 = > string

parameter 2 = > binary

3.parsefloat () converts a string to a floating-point number

A. among the strings . only the first one is valid and the others are invalid.

B. If the string is a valid integer, he returns an integer and does not return a floating-point number.

Second, convert to string type

1.String ( parameters ) can convert any type to a string

Null and undefined: will also be converted to strings, respectively, null and undefined

Boolean type : returns true and false

Numeric type : string of itself

2.toString ()

The calling Format Object . toString ()

The function is to represent the object as a string

Array.tostring () , separated by a string

Boolean.tostring () two value true false

String.tostring () returns itself

Number.tostring ( argument ) returns the string form itself

"Numeric types can use parameters (2-32) to control the output mode "

NOTE:null and undefined do not have the toString () method

Third, convert to Boolean type

Boolean () to convert any type of value to a Boolean value

Convert to False : "", 0, NaN ,undefined, False

All the others are converted to true.

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JavaScript Data type Casting