Type conversion of JS

When a string, The number function is not used as a constructor, it can be treated as a conversion function

such as string (false), number (' 3 '), Boolean ([])

Object (3) = new number (3);

any value other than NULL and undefined has the toString () method

JS automatically detects the expression when executing the program for variable conversion.

Show Conversion variables:

You can use constructors:

String (' op '), Object (), Boolean ([]), Number (' 3 '),

Conversions between types:

Type	String	Digital	Boolean value	Object
Undefined	"Undefined"	NaN	False	Thows TypeError
Null	“”	0	False	Thows TypeError
“”			False	New string ("")
"1.2"		1.2	True	New string ("1.2")
"One"		NaN	True	New string ("one")
0	"0"		False	New Number (0)
-0	"0"		False	New number (-0)
NaN	"NaN"		False	New Number (NaN)
Infinity	"Infinity"		True	New Number (Infinity)
-infinity	"-infinity"		True	New Number (-infinity)
1	' 1 '		True	New Number (1)
{} any object			True
[] arbitrary array		0	True
[8]	"8"	8	True
[' A ']	Join	NaN	True
function		NaN	True

The object is converted to the original value:

All objects are converted to a Boolean value of true, including wrapper objects as well.

objects that are converted to strings and numeric values are called by a method to implement. The trouble is that the JS object has two different ways to convert.

The first method: thetoString () method, which returns a string that reflects the object.

({x:1,y:2}). toString ()//=>[object Object]

The array returns: Each array element is returned and added after the array element , combined into a string.

The toString of the function class returns the function definition syntax;

Date class: Returns a readable date string.

Second method:valueOf ()

This method does not define a specific function;

If the original value is returned with the original value, the object is a composite value, so the object itself is generally returned instead of returning an original value.

Special cases:

Convert object to String:

If the object has the toString method, this method is called if the method returns a raw value and converts the original value to a string.

If the object does not have a toString method, or if this method does not return a raw value, call the ValueOf method if valueOf Returns a raw value that is converted to a string.

If,value,toString cannot return the original value, an error is thrown.

Convert objects to numbers:

If the object has the valueOf method, or if this method does not return a raw value, call the ValueOf method if the valueOf Returns a raw value that is converted to a number.

If the object does not have a valueOf method, then the toString method is called if the method returns a raw value and converts the original value to a number.

If,value,toString cannot return the original value, an error is thrown.

Type conversion of JS