I'm using MDN guide to learn JS and I use scratchpad to try some examples.
If I write
console.log('The value of b is ' + b);
var b;
Why does console.log say "The value of b is -1" ?! It should be undefined
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Ricardo Rocha
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On what page were you opening the scratchpad? Likely it did define a global variable with the value `-1`. Notice that when you take away the `var b;` declaration, the output won't change (or does it?). – Bergi Aug 09 '17 at 08:35
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You are right it's the same even when I remove var b; I open it using Firefox – AbedEl-Rahman Sholi Aug 09 '17 at 08:44
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Yes, Firefox, but don't you have any tabs open? Also try `console.log(window)` and show us what you get – Bergi Aug 09 '17 at 09:02
1 Answers
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Probably you defined the var b before with the value -1.
If you try the above code, you will see that, if the variable is already instantiated and if you declare again the variable without set any value to them, the variable it will not be instantiated.
var b = -1;
console.log(b)
var b;
console.log(b)
Ricardo Rocha
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You are right, and I agree with you, but I have nothing in the code that would make b = -1 !! take a look at the picture : https://ibb.co/jzkNwa – AbedEl-Rahman Sholi Aug 09 '17 at 08:39
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Have you try close the browser and open it again? Sometimes, when you test things in the console, even if you refresh the browser, the variables will be sill on the memory – Ricardo Rocha Aug 09 '17 at 08:44
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Have you sure that is the only file that is been imported in the html? – Ricardo Rocha Aug 09 '17 at 08:47
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I'm sure 100% .. the only thing on the page is what mentioned in the question and this only happens when I try scratchpad, If I write it in HTML file and run it, it works just fine. – AbedEl-Rahman Sholi Aug 09 '17 at 08:50
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Just the last thing, did you tried clean all data from the webpage (like cache, cookies, webstorage..) ? – Ricardo Rocha Aug 09 '17 at 08:58