You can access MySQL session variables as properties of the Session object, as shown in this example:

mysql> SET @myvar = 27;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE PROCEDURE get_session_var() LANGUAGE JAVASCRIPT
    -> AS $$
    $>     console.clear()
    $>     let the_var = session.myvar
    $>     
    $>     console.log("the_var: " + the_var)
    $>     console.log("typeof the_var: " + typeof the_var)
    $> $$;
Query OK, 0 rows affected (0.01 sec)

mysql> CALL get_session_var();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout")\G
*************************** 1. row ***************************
mle_session_state("stdout"): the_var: 27
typeof the_var: number

mysql> SET @myvar = "Something that is not 27";
Query OK, 0 rows affected (0.00 sec)

mysql> CALL get_session_var();
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT mle_session_state("stdout")\G
*************************** 1. row ***************************
mle_session_state("stdout"): the_var: Something that is not 27
typeof the_var: string

1 row in set (0.00 sec)

You can also set session variables by accessing them in the same way, as shown here:

mysql> CREATE PROCEDURE set_session_var(IN x INT) LANGUAGE JAVASCRIPT
    -> AS $$
    $>   session.myvar = x
    $> $$;
Query OK, 0 rows affected (0.01 sec)

mysql> CALL set_session_var(72);
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @myvar;
+--------+
| @myvar |
+--------+
|     72 |
+--------+
1 row in set (0.00 sec)

Session variables accessed as Session properties in JavaScript are created automatically if they do not already exist, as shown in this example:

mysql> CREATE PROCEDURE set_any_var(IN name VARCHAR, IN val INT)
    ->   LANGUAGE JAVASCRIPT
    -> AS $$
    $>   session[name] = val
    $> $$;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @yourvar;
+--------------------+
| @yourvar           |
+--------------------+
| NULL               |
+--------------------+
1 row in set (0.00 sec)

mysql> CALL set_any_var("myvar", 25);
Query OK, 0 rows affected (0.01 sec)

mysql> CALL set_any_var("yourvar", 100);
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @myvar, @yourvar;
+--------+----------+
| @myvar | @yourvar |
+--------+----------+
|     25 |      100 |
+--------+----------+
1 row in set (0.00 sec)

Rules for type conversion from MySQL session variables to JavaScript variables are shown in the following table:

Rules for type conversion from JavaScript variables to MySQL session variables are shown in the following table:

JavaScript stored programs in MySQL 9.3.0 and later support MySQL locales. Localization and internationalization are handled using the Intl global object.

MySQL locale names map to JavaScript locale names by replacing the underscore character with a dash. This can be seen in the following example, which shows how to retrieve the current locale:

mysql> SET @@lc_time_names = "sv_SE";

mysql> CREATE PROCEDURE lc1() LANGUAGE JAVASCRIPT 
mysql>   AS 
mysql>   $$
mysql>     const defaultLocale = Intl.DateTimeFormat().resolvedOptions().locale
mysql>     console.log("Default Locale: ", defaultLocale)
mysql>   $$;

mysql> CALL lc1();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout");
+-----------------------------+
| mle_session_state("stdout") |
+-----------------------------+
|       Default Locale: sv-SE |
+-----------------------------+
1 row in set (0.04 sec)

It is also possible to override the session locale within a JavaScript stored program; here, we show the same number displayed twice in succession using a different locale each time:

mysql> SET @@lc_time_names = "fr_FR";
Query OK, 0 rows affected (0.01 sec)

mysql> CREATE PROCEDURE lc2() LANGUAGE JAVASCRIPT 
mysql>   AS 
mysql>   $$
mysql>     const defaultLocale = Intl.DateTimeFormat().resolvedOptions().locale
mysql>     const n = 1234567.89;
mysql>     console.log("Default Locale (", defaultLocale, "): ", n.toLocaleString());
mysql>     console.log("ja_JP Locale: ", n.toLocaleString("ja-JP"));
mysql>   $$;
Query OK, 0 rows affected (0.01 sec)

mysql> CALL lc2();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout");
+--------------------------------------+
| mle_session_state("stdout")          |
+--------------------------------------+
| Default Locale (fr-FR): 1 234 567,89
  Using ja_JP locale: 1,234,567.89     |
+--------------------------------------+
1 row in set (0.04 sec)

You can use toLocaleString() and other such methods to specify the locale for numbers and dates. For currency and other special numeric values, create an instance of NumberFormat having the appropriate properties.

A JavaScript stored program continues to use by default the session locale setting that was in effect the first time it was invoked is executed during a given session remains in effect, even if the session locale setting is changed, until the session is reset. (This does not affect the result of toLocaleString() or NumberFormat called with an explicit locale.) If lc_time_names is updated, call mle_session_reset() to cause any existing stored programs to use the new locale setting by default instead. An example is shown here:

mysql> SELECT @@lc_time_names;
+-----------------+
| @@lc_time_names |
+-----------------+
| fr_FR           |
+-----------------+
1 row in set (0.00 sec)

mysql> CALL lc1();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout");
+-----------------------------+
| mle_session_state("stdout") |
+-----------------------------+
|       Default Locale: fr-FR |
+-----------------------------+
1 row in set (0.04 sec)

mysql> SET @@lc_time_names = "ja_JP";
+-----------------+
| @@lc_time_names |
+-----------------+
| fr_FR           |
+-----------------+
1 row in set (0.00 sec)

mysql> CALL lc1();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout");
+-----------------------------+
| mle_session_state("stdout") |
+-----------------------------+
|       Default Locale: fr-FR |
+-----------------------------+
1 row in set (0.04 sec)

mysql> SELECT mle_session_reset();
+------------------------------------------+
| mle_session_reset()                      |
+------------------------------------------+
| The session state is successfully reset. |
+------------------------------------------+
1 row in set (0.01 sec)

mysql> CALL lc1();
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT mle_session_state("stdout");
+-----------------------------+
| mle_session_state("stdout") |
+-----------------------------+
|       Default Locale: ja-JP |
+-----------------------------+
1 row in set (0.04 sec)