The role of!! in js

The function of !! in

js is:

!! is generally used to convert the following expressions into Boolean data (boolean)

=== indicates that all types are equal (just write an if to test it yourself) )

!== means you don’t want to wait and include the type (write an if the same way)

|| or means

!! Generally used to convert the following expression into Boolean data (boolean) because javascript It is a weakly typed language (variables do not have a fixed data type), so sometimes it is necessary to force conversion to the corresponding type,

Similar example: a=parseInt("1234") a="1234"+0 //Convert to number b =1234+"" //Convert to string c=someObject.toString() //Convert object to string. Type 1 and Type 4 are explicit conversions, and

2 and 3 are implicit conversions to Boolean type. The conversion, JavaScript convention is similar to c, the rules are: false, undefined, null, 0, "" is false, true, 1, "somestring", [Object] is true