ReferenceError variable is not defined

Question

I met this issue sometimes but still don t know what causes it   I have this script in the page     function        var value    10         But the browser says  ReferenceError  value is not defined   However if I go to the browser console and input either  10   or  var value    10     either of them can return 10  What is the problem with my script

User · Answer

Got the error  in the function init  with the following code      use strict     var hdr    function init       called on load     hdr   document getElementById  hdr            while using the stock browser on a Samsung galaxy Fame   crap phone which makes it a good tester   - userAgent   Mozilla 5 0  Linux  U  Android 4 1 2  en-gb  GT-S6810P Build JZO54K  AppleWebKit 534 30  KHTML  like Gecko  Version 4 0 Mobile Safari 534 30  The same code works everywhere else I tried including the stock browser on an older HTC phone - userAgent   Mozilla 5 0  Linux  U  Android 2 3 5  en-gb  HTC WildfireS A510e Build GRJ90  AppleWebKit 533 1  KHTML  like Gecko  Version 4 0 Mobile Safari 533 1  The fix for this was to change  var hdr     to   var hdr   null

User · Answer

Variables are available only in the scope you defined them  If you define a variable inside a function  you won t be able to access it outside of it   Define variable with var outside the function  and of course before it  and then assign 10 to it inside function   var value    function       value    10       console log value      10   Note that you shouldn t omit the first line in this code  var value    because otherwise you are assigning value to undefined variable  This is bad coding practice and will not work in strict mode  Defining a variable  var variable   and assigning value to a variable  variable   value   are two different things  You can t assign value to variable that you haven t defined   It might be irrelevant here  but   function       is a shortcut for   document  ready function        which executes a function as soon as document is loaded  If you want to execute something immediately  you don t need it  otherwise beware that if you run it before DOM has loaded  value will be undefined until it has loaded  so console log value   placed right after   function       will return undefined  In other words  it would execute in following order   var value  console log value   value    10     See also    What is the scope of variables in JavaScript  I  39 ve Heard Global Variables Are Bad  What Alternative Solution Should I Use

User · Answer

It s declared inside a closure  which means it can only be accessed there   If you want a variable accessible globally  you can remove the var     function        value    10       value      10    This is equivalent to writing window value    10

[javascript] ReferenceError: variable is not defined

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