How do I change the value of a global variable inside of a function

Question

I am using JavaScript and I create a global variable  I define it outside of a function and I want to change the global variable value from inside a function and use it from another function  how do I do this

User · Answer

var a   10   myFunction a    function myFunction a      window  a     20     or window a    alert  Value of  a  outside the function     a     outputs 20   With  window  variableName   or window variableName you can modify the value of a global variable inside a function

User · Answer

var a   10   myFunction     function myFunction       a   20     alert  Value of  a  outside the function     a     outputs 20

User · Answer

Just reference the variable inside the function  no magic  just use it s name  If it s been created globally  then you ll be updating the global variable   You can override this behaviour by declaring it locally using var  but if you don t use var  then a variable name used in a function will be global if that variable has been declared globally   That s why it s considered best practice to always declare your variables explicitly with var  Because if you forget it  you can start messing with globals by accident  It s an easy mistake to make  But in your case  this turn around and becomes an easy answer to your question

User · Answer

lt script gt  var x   2    X is global and value is 2   function myFunction      x   7    x is local variable and value is 7      myFunction     alert x     x is gobal variable and the value is 7  lt  script gt

User · Answer

Just use the name of that variable    In JavaScript  variables are only local to a function  if they are the function s parameter s  or if you declare them as local explicitely by typing the var keyword before the name of the variable   If the name of the local value has the same name as the global value  use the window object  See this jsfiddle   x000D   x000D  x   1  x000D  y   2  x000D  z   3  x000D   x000D  function a y    x000D       y is local to the function  because it is a function parameter x000D    console log  local y  should be 10    y      local y through function parameter x000D    y   3     will only overwrite local y  not  global  y x000D    console log  local y  should be 3    y      local y x000D       global value could be accessed by referencing through window object x000D    console log  global y  should be 2    window y     global y  different from local y    x000D   x000D    var x     makes x a local variable x000D    x   4     only overwrites local x x000D    console log  local x  should be 4    x      local x x000D     x000D    z   5     overwrites global z  because there is no local z x000D    console log  local z  should be 5    z      local z  same as global x000D    console log  global z  should be 5 5    window z  z     global z  same as z  because z is not local x000D    x000D  a 10   x000D  console log  global x  should be 1    x      global x x000D  console log  global y  should be 2    y      global y x000D  console log  global z  should be 5    z      global z  overwritten in function a x000D   x000D   x000D    Edit  With ES2015 there came two more keywords const and let  which also affect the scope of a variable  Language Specification

[javascript] How do I change the value of a global variable inside of a function

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