Typescript variable declaration - type assertion

When the type is not given ,TypeScript The compiler uses type inference to infer types .

If the type cannot be inferred due to lack of declaration , Then its type is regarded as the default dynamic any type .

as follows ：

let num = 12;    //  The type is inferred as  number
console.log("num  The value of the variable is  " + num); 
num = "abcde";  

Report errors ：

First, the variables are declared num, And assignment 12;

Because the variable declaration does not specify a type , therefore , The program applies type inference to determine that the data type of the variable is number.

Next , Trying to give a variable num The assignment is abcde when , Compile error , Because the variable has been set to number type .