what is the precedence of datatype while comparison .

Question

User2102072086 posted

hi

    when I compair in javascript  like so , then it converts one type to another type. which is based on precedence. can I get link of that precedence.

if ("2"<3)

{

}

Answer 1

User1535942433 posted

Hi rajemessage,

As far as I think,the precedence of datatype from highest to lowest is user-defined data types (highest)>sql_variant>xml>datetimeoffset>datetime2>datetime>smalldatetime>date>time>float>real>decimal>money>smallmoney>bigint>int>smallint>tinyint>bit>ntext>text>image>timestamp>timestamp>nvarchar (including nvarchar(max) )>nchar>varchar (including varchar(max) )>char>varbinary (including varbinary(max) >binary (lowest).

More details,you could refer to below article:

https://docs.microsoft.com/en-us/sql/t-sql/data-types/data-type-precedence-transact-sql?view=sql-server-ver15

Best regards,

Yijing Sun

Answer 2

User2102072086 posted

question is for javascript not for tsql

Answer 3

User1535942433 posted

Hi rajemessage,

 when I compair in javascript  like so , then it converts one type to another type. which is based on precedence. can I get link of that precedence.

Accroding to your description,you have converted one type to another type,which is based on the size of the type instead of precedence.

Implicit Casting is converting a smaller type to a larger type size and Explicit Casting is converting a larger type to a smaller size type.

About the size of datatype,you could refer to below article:

https://www.w3schools.com/cs/cs_type_casting.asp

Besides,the operator have the precedence,you could refer to below article:

https://docs.w3cub.com/javascript/operators/operator_precedence/

Best regards,

Yijing Sun

Answer 4

User-474980206 posted

Here is a good explanation 

https://2ality.com/2019/10/type-coercion.html

but in your sample

   a < 3

if a is a string it will try to convert to number, if it can, then numeric compare, if it can not then string compare

   "1" < 3  // numeric compare - true
   "a" < 3  // string compare    - false
   "\t" < 3  // string compare    - true

so in general javascript does the right thing.

note: the switch does a "===", match value and type. this was probably a design flaw, but too late to fix.

switch ("1")  {
     case 1: 
          console.log("match"); // no
          break;
     case "1":   
          console.log("match"); // yes
          break;
}

Answer 5

User2102072086 posted

the link is of c# and i am talking about javascript. thank u.

Answer 6

User1535942433 posted

Hi rajemessage,

As far as I think,javascript data types could mutual convert.If you need to convert to string type,you could add .tostring().Also,you could convert other type.Most of the time, operators and functions automatically convert the values given to them to the right type.When the left and right value have differernt type,the comparison have errors.

Just like:

 <script>
        function compare() {
            var x = true;
            var y = Number(x);
            if (y < 3) { alert(y) };
            var z = 1;
            var e = Boolean(z);
            if (e < 3)
            { alert(3) }
            else { alert(e) };
            var n = "2";
            var m = parseInt(n);
            if (m < 3) { alert(m) };
        }
</script>

So,I don't know what your meaings of the precedence of datatype while comparison.Could you tell us more details of your reqiurment?

More details,you could refer to below article:

https://javascript.info/type-conversions

Best regards,

Yijing Sun

Answer 7

User753101303 posted

Hi,

Try https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality#Description which points to a spec (11.9.3).

Answer 8

User2102072086 posted

https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion

Answer 9

User1535942433 posted

Hi rajemessage,

JavaScript is loosely typed language and most of the time operators automatically convert a value to the right type but there are also cases when we need to explicitly do type conversions.There are two most common data conversions :

1.Converting Values to String

2.Converting Values to Numbers

Implicit Conversion:

There are various operator and functions in JavaScript which automatically converts a value to the right type like alert() function in JavaScript accepts any value and convert it into a string.

explicit Conversion:

Converting Values to Strings:

String() or toString() function can be used in JavaScript to convert a value to a string.

Converting Values to Numbers:

We can use Number() function in JavaScript to convert a value to a Number. It can convert any numerical text and boolean value to a Number. In case of strings of non-numbers it will convert it to a NaN(Not a Number).

Best regards,

Yijing Sun