How to determine the type of js object? Detailed explanation of basic type conversion in js

1. Type conversion

1. Convert to string toString() or string() or ""
null and undefined cannot use toString () will report an error.
2. Convert to Boolean value Boolean() or! !
Five falsy values: 0 NaN ” null undefined Except for these five, other Boolean values ​​are true
All object Boolean values ​​are true
3. Convert to number

*Number('1')===1*parseInt("1",10)===1不加第二个参数时，默认为十进制.
*parseFloat('1.23')===1.23*'1'-0===1*+'1'===1或者+'-1'===1

2. Memory graph

1. Memory and external storage
The memory reads data from the external storage and processes it
js engine After getting the allocated memory, the memory will be divided into code area and data area as shown above.
Let’s focus on the data area:
1. Original data types are stored in stack memory, and complex data The type is stored in the heap memory
(so the value of the original data type stored in the variable, the address of the complex data type stored in the variable, the changed address is stored in the stack memory and points to the complex data type in the heap memory)
2. Operations on primitive data types are all worthwhile operations, and operations on complex data types are operations on the device address

Note:

var a={n:1}var b=a;
a.x=a={n:3};(这句话先对a.x进行操作，然后在对a=
{}操作)
那么
a.x===undefined;
b.x==={n:3}

2. Garbage collection mechanism

If an object is not referenced , it is garbage and will be recycled.

3. Deep and shallow copy

Those that do not affect each other after copying are called deep copies, such as simple data types The copy

that affects each other is called shallow copy, such as the copy of an object.

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