and transformation of data types js

1. In case the object operator

Conversion rule is:

1) first calls itself valueOf () method, raw data, return, or 2);

2) then calls itself toString () method, if not the original data, Uncaught TypeError;

There is one exception: Instead Date object, first call toString (), after a call valueOf ().

There obj = {
    valueOf(){ return 5; },    
    toString() { return 'hello'; }
}
1 + obj; //  6;
"1" + obj; //  "15"

2. In case of the original data Operators

And transformation of:

1) If the value of the operator is required, calls valueOf ();

2) If the operator requires string, call toString ();

3) If either value may be a string, a priority call valueOf ();

// example of Boolean values 
( to true ) .valueOf (); // . 1 
( to true ) .toString (); // "to true"

1+true; // 2
"1" + true; // 1true

3. String () function in case of tool objects

And transformation of:

1) first call toString (), to determine whether to return the original data; if it is, the end, or 2)

2) call valueOf ()

There obj = {
    valueOf(){ return 5; },    
    toString() { return 'hello'; }
};
String(obj); // "hello"

4. Number () function in case of tool objects

And transformation of:

1) first call valueOf () method, if the return to the original data, ending; otherwise 2)

2) call toString () method

There obj = {
    valueOf(){ return 5; },    
    toString() { return 'hello'; }
};
Number(obj); // 5