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Cannot Determine is Variable is "undefined"


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I an trying to determine if a cookie exists using the following code:

const json_str=Cookies.get("Auto_Select_051969");
if (!(json_str in window)) {

When it gets to the parse I get the error:

Uncaught SyntaxError: "undefined" is not valid JSON
    at JSON.parse (<anonymous>)
    at cookie_mgmt.js:16:11

'create_cookie()' is not executed. If 'json_str' is undefined, per the error, how can it fail the 'if' test?

I also tried:

if (typeof(json_str)=="undefined") {

Which also fails the 'if' test.

Edited by gw1500se
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I finally got it working but I can't explain how/why. I did:


The output was "true" which I expected. I then edited the line by changing 'console.log' to 'if' and changed the ';' to '{' and the thing started to work. :confused:

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