Creating variable array object with for loop

Question

Creating variable array object with for loop

I have a for loop that pulls data from a MySQL server. I would like the four values to be put into variables so I can use them later. Here's the code I have; for some reason, it says thev is undefined?

create();

function create(){

for(var i=0;i<4;i++){

        var thev=[];

        client.query('SELECT curattend FROM table1 WHERE ind=?',[i], function(err,result){
        thev[i] = result[0].curattend;

        });

        }
        return thev;
}
  console.log(thev[2]);

I would appreciate any advice on this problem.

javascript
mysql
node.js
for-loop

Answer 1

There are a lot of problems here.

thev is local to create. You don’t assign the return value of create to anything, so it’s still not going to be defined.
var thev = []; should not be inside the for loop. It’ll only end up containing one element. Or it would, but…
The callback to query is not just there for fun; it’s an asynchronous call, and is 100% sure to not have happened by the time you actually return from the function.

I would just do it using the async library:

function range(start, end) {
    var result = [];

    while(start < end) {
        result.push(start);
        start++;
    }

    return result;
}

async.map(range(0, 4), function(i, callback) {
    client.query('SELECT curattend FROM table1 WHERE ind = ?', [i], function(err, result) {
        if(err) return callback(err);
        callback(null, result[0].curattend);
    });
}, function(err, thev) {
    // Continue
});