How can i assign value to a global variable in node.js?

Question

I met a problem recently: How can i assign value to a global variable?

when i try to return a, i found that is undefined, and the "value" i wanna to assign to it is not undefined.

my code is like this:

module.exports = function (jsonStr) {
    var a;
    request(main_url, function(error, response, html) { 
        if(!error) {
           ...
           request(sub_url, function(error, response, html) { 
               if(!error) {
                  ...
                  a = value;
                  ...
               }
           }
         }    
    } 
    return a;   
});

replace "var a" with "". but, btter, don't use globals; tack the stuff onto `exports` as needed. — dandavis, Oct 06 '15 at 16:42
That is because `a = value` gets executed asynchronously (the assignment happens **after** your function on `module.exports` finishes execution). What you should do is have a callback on your function that has `a` as an argument. (For example, `function(jsonStr, callback)`) — JCOC611, Oct 06 '15 at 16:42
http://stackoverflow.com/questions/32407269/why-cant-i-see-this-json-in-the-console — Soren, Oct 06 '15 at 16:45
@JCOC611 Omg, after? ah, that's why, i will check my logic again. Thank you ! — Leyla Lee, Oct 06 '15 at 16:46
@JCOC611 sorry, i tried, but i still failed to return a, i was totally confused about how to return it. T.T can u help me? — Leyla Lee, Oct 07 '15 at 10:03

score 0 · Answer 1 · edited May 23 '17 at 11:58

The problem there is that your request function is asynchronous, and then, the return a statement will occur before you set a = value.

One way to achieve what you want is by using the asyncawait library, something like:

module.exports = async(function (jsonStr) {
    var a;
    var sub_url = await(request(main_url));
    a = await(request(sub_url));
    return a; 
});

Take a look at this QA.

How can i assign value to a global variable in node.js?

1 Answers1