NodeJS - How can I check if a MySQL result is undefined/empty?-CodePudding

Does anyone know how to check if a NodeJS MySQL result is null/empty? What I'm trying to do is (very succinctly explained) to check if result 5 is empty or not, and if it's not, then execute an action (console.log in this case).

This is the code without all the details, to simplify things, but when executing it I get that "result" is not defined

           con.query("SELECT tag, message FROM list1", function (err, result) {
            if (err) {
              console.log('Error: '   err)
            }
          });
        
          if(!result[5] == undefined) {
              console.log('Result 5 exists')
          }

CodePudding user response：

I highly recommend you to use this pattern.

con.query('SELECT tag, message FROM list1', [info] function(err, row, fields) {
  if(err) {
    return console.log('Error1');
  } else if (!row.length) {                                                   
    return console.log('Error2');
  } else if (!row[0].something) {
    return console.log('Error3');
  }

  console.log('Works');
})

It's using a "falsy" check for row[0]. something which will return false if the value is undefined, null or an empty string. It also fixes the injection attack vector.

CodePudding user response：

In the if statement at the bottom, use typeof result[5] !== 'undefined'.

Your current method checks if the value of result[5] is equal to undefined, but will crash if result[5] does not exist. Checking the type will return 'undefined' if the variable does not exist.

edited code:

con.query("SELECT tag, message FROM list1", function (err, result) {
    if (err) {
        console.log('Error: '   err);
    }
});
    
if(typeof result[5] !== 'undefined') {
    console.log('Result 5 exists');
}