mr_michael mr_michael - 3 months ago 8
JSON Question

Data not being added to JSON object inside of anonymous function

When returning the JSON object items_json, using the express method res.json(items_json), I have run into an issue. When the express method res.json(items_json) is called at POSITION #1 in the code below, the function works perfectly. However, when res.json(items_json) is called at POSITION #2 instead of #1, the JSON object returned is empty:

{
"example_key_object": []
}


I want to have res.json(items_json) in POSITION #2 so I can add a loop. Why is the JSON response empty when in POSITION #2 but works fine when in POSITION #1? (Context for code below: res.json(items_json) is never in both POSITION #1 & #2)

app.get('/example_apiurl', function(req, res) {

var items_json = {}
var key_object = 'example_key_object';
items_json[example_key_object] = [];

var item_str;
var data;
var url = "example.com";

request(url, function(error, response, html){
if(!error){
var $ = cheerio.load(html);

/*
some irreverent logic to get var items_clean_st
*/

item_str = items_clean_st.substring(x,y);
data = {
locationID: 2,
item: item_str
};
items_json[key_object].push(data);
res.json(items_json) //POSITION #1 //returns correctly!
}
})
res.json(items_json) //POSITION #2 //empty :(
}
})

Answer

You are passing an anonymous function as a parameter to another function called request. I don't know exactly what happens with this anonymous function, but I'm guessing that it is called at a future time in response to some browser event, such as an AJAX request completing.

Therefore, it is likely that the call at POSITION #2 happens before the call at POSITION #1.