How to get value from unknown object property?

Question

I have an issue with extracting value from object. I want to check if my SQL table have the asked row:

var checkRow = function(connection,chekedColumn,chekParam, checkVal){
    connection.query('SELECT EXISTS(SELECT '+ chekedColumn +' FROM asterisk.users where ' +chekParam+'='+checkVal+')', function (err, rows) {
        if(err) console.log('SQL suerry error')
        else {
            console.log(rows[0]); // output: { 'EXISTS(SELECT id FROM asterisk.users where name=1600)': 1 }
            return (rows[0]);
        }; 
    }); 
};

but returned value from query is an object, and return(rows[0]) give just [object object] output. How can I extract value of this object?

As I know that in javascript access object with dot (.) keyword don't use this rows[0] try this if I'm not wrong rows.0 — user2727841, Oct 03 '13 at 06:13
rows[0] is fine, rows.0 is not, 0 is not valid property name. See valid property names for access via . [here](http://stackoverflow.com/questions/1661197/valid-characters-for-javascript-variable-names). — user568109, Oct 03 '13 at 06:23
You cannot do return from asynchronous function to get the value. You should call your function to process the returned value from inside the query. — user568109, Oct 03 '13 at 06:27
@user2727841 decimal digits alone do not form valid property names. You can't use it via `.`. — user568109, Oct 03 '13 at 06:33

Dmitry Matveev · Answer 1 · 2013-10-03T06:30:05.473

2

You can use

Object.keys(obj)

to get the values of the object. See api reference for more info.

EDIT:

Just to elaborate abit more on this... how you'd go about getting it out is this.

// get the keys of the source
var keys = Object.keys( source );
// loop through the keys
for ( var i = 0; i < keys.length; i++ ) {
  var key = keys[i];
  var value = source[key];

  //do something with value
}

edited Oct 03 '13 at 06:30

answered Oct 03 '13 at 06:22

Dmitry Matveev

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var keys=Object.keys(rows[0]); var key=keys[0]; console.log(rows[key]);// output : undefined – Alex Cebotari Oct 03 '13 at 06:42
console.log(key);// output: EXISTS(SELECT id FROM asterisk.users where name=1600) – Alex Cebotari Oct 03 '13 at 06:44
console.log(rows[0].key);// output: undefined – Alex Cebotari Oct 03 '13 at 06:46
console.log(key); <--- this is the value inside the unknown object property (I assume this is what is getting assigned as a parameter to a query callback function which is the answer to your question). If the value is not what you expect I suggest you debug your code and see what happens, consider rephrasing your question since this is a different matter altogether. There is a good tool for debugging node apps which is called [NodeWebKit](https://github.com/rogerwang/node-webkit) – Dmitry Matveev Oct 03 '13 at 08:06

score 0 · Answer 2 · answered Oct 03 '13 at 07:06

The output is an object which you don't know. So try either:

console.log("Result: %j", rows[0]);
console.log(JSON.stringify(rows[0]));
console.log(require('util').inspect(rows[0], false, null));

to view the structure. After you know the keys, use it to access the data.

score 0 · Answer 3 · answered Oct 04 '13 at 07:38

Thanks all for helps and for your ideas. Dmitry Matveev help me to understand how to identify object properties(Objekt.keys()). And thanks to user568109 for reminding of asynchronous function, so I use callback.
Final code:

var checkRow = function(connection,chekedColumn,chekParam, checkVal,callback){
    connection.query('SELECT EXISTS(SELECT '+ chekedColumn +' FROM asterisk.users where ' +chekParam+'='+checkVal+')', function (err, rows) {
                if(err) console.log('SQL suerry error')
                else {
                   var keys=Object.keys(rows[0]);
                   keys.forEach(function(key) {
                       callback(rows[0][key]);
                     });
                    }; 
        }); 

};

And for using this functions we need to call it like:

checkRow(connection,'id','name',name,function(value){
 console.log(value)
})

everyone on stackoverflow would love you if you start marking answers as accepted that helped you to figure out your problem ;) — Dmitry Matveev, Jan 17 '16 at 21:44

How to get value from unknown object property?

3 Answers3