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javascript - i want to create a function that returns the execution result of connectionquery

I want to achieve 
console.log (
    m_sql (
        "SELECT * FROM accounts WHERE user =?;", ["Jhon"]
    ) .results [0] .mail_address
);


SQL statement with Node.js likem_sql ()Pass it to the function and send the execution result of the SQL statementm_sql ()Receive as the return value of the function.
thism_sql ()I want to make a function.

Where i am stumbling 
const mysql = require ("mysql");
const connection = mysql.createConnection ({{
    host: "localhost",
    user: "root",
    password: "toor",
    database: "test"
});
/ * ================================================ ============= * /
function m_sql (code, argv) {
    var ret;
    new Promise ((resolve, reject) =>{
        // Since connection.query is an asynchronous function, we are using a Promise.
        connection.query (code, argv,
            (error, results, fields) =>{
                resolve ({{
                    error: error,
                    results: results,
                    fields: fields
                });
            }
        );
    }). then (data =>{
        ret = data;
        console.log (data);
        // =>SQL statement execution result
        console.log (ret);
        // =>SQL statement execution result
        // Here, the execution result of the SQL statement is safely stored in ret,
    });
    // Here ret is undefined
    console.log (ret);
    // =>undefined
    return ret;
}
console.log (m_sql ("SELECT * FROM auth;"));
// =>undefined
what I want to know
  • How can iretHolds the execution result of the SQL statementreturnCan you do it?
What I researched/tried
  • Pass by reference
    Passing JavaScript by reference was confusing and I couldn't do it.
    There is also an article that passing by reference does not exist.
Environment/version
  • OS Windows 10 Home 64bit
  • Node.js v12.16.1
  • SQL 10.5.5-MariaDB
javascript sql node.js functions mariadb
  • Answer # 1

    PromiseI think there is a misunderstanding about the behavior of.retThe problem I'm having with is "not assigning" instead of "not holding". It may not be intuitive, but this code is processed in the following order:

          function m_sql (code, argv) {
/ * 1 */var ret;// Unassigned
            new Promise ((resolve, reject) =>{
/*3*/ connection.query (code, argv,
/ * 4 */(error, results, fields) =>{
/ * 5 */resolve ({{
                            error: error,
                            results: results,
                            fields: fields
                        });
                    }
                );
            }). then (data =>{
/ * 6 */ret = data;// Assigned here
            });
            // Because it is not said "Wait for` Promise` ", it will be skipped so far
/ * 2 */return ret;// Not assigned
        }
        console.log (m_sql ("SELECT * FROM auth;"));// Output in step 2

    To solve thism_sql ()Asynchronize itself (PromiseLet's do it.

    // Make the return value of the function `Promise` by prefixing it with` async`
async function m_sql (code, argv) {
    // No need for `var ret`
    // Wait for the `Promise` to be resolved by prepending the` await` to the `new Promise`
    const data = await new Promise ((resolve, reject) =>{
        connection.query (code, argv,
            (error, results, fields) =>{
                resolve ({{
                    error: error,
                    results: results,
                    fields: fields
                });
            }
        );
    // When you reach here, the completion of `Promise` processing is guaranteed
    // `.then (...)` is unnecessary
    return data;// Can return `data` directly
}

    Keep in mind when calling this function (asynchronous function)awaitWithPromiseLet's wait for the resolution:

    // Using `await` outside the function is called" Top-level await "
console.log (await m_sql ("SELECT * FROM auth;"));

    Older node versions (14.7.0 and earlier) don't support Top-level await, so the whole thingasync mainMust be enclosed in a function:

    async function main () {
    // Put the whole process here
    console.log (await m_sql ("SELECT * FROM auth;"));
}
main ();

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