Accessing variables from other functions without using global variables

Question

I ve heard from a variety of places that global variables are inherently nasty and evil  but when doing some non-object oriented Javascript  I can t see how to avoid them  Say I have a function which generates a number using a complex algorithm using random numbers and stuff  but I need to keep using that particular number in some other function which is a callback or something and so can t be part of the same function    If the originally generated number is a local variable  it won t be accessible from  there  If the functions were object methods  I could make the number a property but they re not and it seems somewhat overcomplicated to change the whole program structure to do this  Is a global variable really so bad

User · Answer

What you re looking for is technically known as currying   function getMyCallback randomValue        return function otherParam                return randomValue   otherParam   or whatever it is you are doing            var myCallback   getMyCallBack getRand     alert myCallBack 1    alert myCallBack 2      The above isn t exactly a curried function but it achieves the result of maintaining an existing value without adding variables to the global namespace or requiring some other object repository for it

User · Answer

If there s a chance that you will reuse this code  then I would probably make the effort to go with an object-oriented perspective   Using the global namespace can be dangerous -- you run the risk of hard to find bugs due to variable names that get reused   Typically I start by using an object-oriented approach for anything more than a simple callback so that I don t have to do the re-write thing  Any time that you have a group of related functions in javascript  I think  it s a candidate for an object-oriented approach

User · Answer

I think your best bet here may be to define a single global-scoped variable  and dumping your variables there   var MyApp          Globally scoped object  function foo        MyApp color    green      function bar        alert MyApp color      Alerts  green       No one should yell at you for doing something like the above

User · Answer

To make a variable calculated in function A visible in function B  you have three choices    make it a global  make it an object property  or pass it as a parameter when calling B from A    If your program is fairly small then globals are not so bad   Otherwise I would consider using the third method   function A         var rand num   calculate random number        B rand num      function B r        use rand num r

User · Answer

If another function needs to use a variable you pass it to the function as an argument   Also global variables are not inherently nasty and evil   As long as they are used properly there is no problem with them

User · Answer

What you re looking for is technically known as currying   function getMyCallback randomValue        return function otherParam                return randomValue   otherParam   or whatever it is you are doing            var myCallback   getMyCallBack getRand     alert myCallBack 1    alert myCallBack 2      The above isn t exactly a curried function but it achieves the result of maintaining an existing value without adding variables to the global namespace or requiring some other object repository for it

User · Answer

What you re looking for is technically known as currying   function getMyCallback randomValue        return function otherParam                return randomValue   otherParam   or whatever it is you are doing            var myCallback   getMyCallBack getRand     alert myCallBack 1    alert myCallBack 2      The above isn t exactly a curried function but it achieves the result of maintaining an existing value without adding variables to the global namespace or requiring some other object repository for it

User · Answer

I found this to be extremely helpful in relation to the original question   Return the value you wish to use in functionOne  then call functionOne within functionTwo   then place the result into a fresh var and reference this new var within functionTwo  This should enable you to use the var declared in functionOne  within functionTwo   function functionOne       var variableThree   3    return variableThree     function functionTwo       var variableOne   1    var var3   functionOne       var result   var3 - variableOne     console log variableOne     console log var3     console log  functional result      result      functionTwo

User · Answer

To make a variable calculated in function A visible in function B  you have three choices    make it a global  make it an object property  or pass it as a parameter when calling B from A    If your program is fairly small then globals are not so bad   Otherwise I would consider using the third method   function A         var rand num   calculate random number        B rand num      function B r        use rand num r

User · Answer

Another approach is one that I picked up from a Douglas Crockford forum post http   bytes com topic javascript answers 512361-array-objects   Here it is     Douglas Crockford wrote   Jul 15  06    If you want to retrieve objects by id  then you should use an object  not an array  Since functions are also objects  you could store the members in the function itself    function objFacility id  name  adr  city  state  zip         return objFacility id               id  id          name  name          adr  adr          city  city          state  state          zip  zip           objFacility  wlevine    Levine    23 Skid Row    Springfield    Il   10010      The object can be obtained with    objFacility wlevine   The objects properties are now accessable from within any other function

User · Answer

If another function needs to use a variable you pass it to the function as an argument   Also global variables are not inherently nasty and evil   As long as they are used properly there is no problem with them

User · Answer

To make a variable calculated in function A visible in function B  you have three choices    make it a global  make it an object property  or pass it as a parameter when calling B from A    If your program is fairly small then globals are not so bad   Otherwise I would consider using the third method   function A         var rand num   calculate random number        B rand num      function B r        use rand num r

User · Answer

What you re looking for is technically known as currying   function getMyCallback randomValue        return function otherParam                return randomValue   otherParam   or whatever it is you are doing            var myCallback   getMyCallBack getRand     alert myCallBack 1    alert myCallBack 2      The above isn t exactly a curried function but it achieves the result of maintaining an existing value without adding variables to the global namespace or requiring some other object repository for it

User · Answer

If another function needs to use a variable you pass it to the function as an argument   Also global variables are not inherently nasty and evil   As long as they are used properly there is no problem with them

User · Answer

Another approach is one that I picked up from a Douglas Crockford forum post http   bytes com topic javascript answers 512361-array-objects   Here it is     Douglas Crockford wrote   Jul 15  06    If you want to retrieve objects by id  then you should use an object  not an array  Since functions are also objects  you could store the members in the function itself    function objFacility id  name  adr  city  state  zip         return objFacility id               id  id          name  name          adr  adr          city  city          state  state          zip  zip           objFacility  wlevine    Levine    23 Skid Row    Springfield    Il   10010      The object can be obtained with    objFacility wlevine   The objects properties are now accessable from within any other function

User · Answer

Consider using namespaces    function         var local var    foo       global var    bar      this global var and window global var also work      function local function          global function   function               Both local function and global function have access to all local and global variables   Edit  Another common pattern   var ns    function            local stuff     function foo          function bar          function baz         this one stays invisible         stuff visible in namespace object     return           foo   foo          bar   bar                The returned properties can now be accessed via the namespace object  e g  ns foo  while still retaining access to local definitions

User · Answer

I found this to be extremely helpful in relation to the original question   Return the value you wish to use in functionOne  then call functionOne within functionTwo   then place the result into a fresh var and reference this new var within functionTwo  This should enable you to use the var declared in functionOne  within functionTwo   function functionOne       var variableThree   3    return variableThree     function functionTwo       var variableOne   1    var var3   functionOne       var result   var3 - variableOne     console log variableOne     console log var3     console log  functional result      result      functionTwo

User · Answer

I don t know specifics of your issue  but if the function needs the value then it can be a parameter passed through the call   Globals are considered bad because globals state and multiple modifiers can create hard to follow code and strange errors   To many actors fiddling with something can create chaos

User · Answer

I think your best bet here may be to define a single global-scoped variable  and dumping your variables there   var MyApp          Globally scoped object  function foo        MyApp color    green      function bar        alert MyApp color      Alerts  green       No one should yell at you for doing something like the above

User · Answer

If there s a chance that you will reuse this code  then I would probably make the effort to go with an object-oriented perspective   Using the global namespace can be dangerous -- you run the risk of hard to find bugs due to variable names that get reused   Typically I start by using an object-oriented approach for anything more than a simple callback so that I don t have to do the re-write thing  Any time that you have a group of related functions in javascript  I think  it s a candidate for an object-oriented approach

User · Answer

If there s a chance that you will reuse this code  then I would probably make the effort to go with an object-oriented perspective   Using the global namespace can be dangerous -- you run the risk of hard to find bugs due to variable names that get reused   Typically I start by using an object-oriented approach for anything more than a simple callback so that I don t have to do the re-write thing  Any time that you have a group of related functions in javascript  I think  it s a candidate for an object-oriented approach

User · Answer

Consider using namespaces    function         var local var    foo       global var    bar      this global var and window global var also work      function local function          global function   function               Both local function and global function have access to all local and global variables   Edit  Another common pattern   var ns    function            local stuff     function foo          function bar          function baz         this one stays invisible         stuff visible in namespace object     return           foo   foo          bar   bar                The returned properties can now be accessed via the namespace object  e g  ns foo  while still retaining access to local definitions

User · Answer

I don t know specifics of your issue  but if the function needs the value then it can be a parameter passed through the call   Globals are considered bad because globals state and multiple modifiers can create hard to follow code and strange errors   To many actors fiddling with something can create chaos

User · Answer

You can completely control the execution of javascript functions  and pass variables between them  using custom jQuery events    I was told that this wasn t possible all over these forums  but I got something working that does exactly that  even using an ajax call      Here s the answer  IMPORTANT  it s not the checked answer but rather the answer by me  Emile     How to get a variable returned across multiple functions - Javascript jQuery

User · Answer

I think your best bet here may be to define a single global-scoped variable  and dumping your variables there   var MyApp          Globally scoped object  function foo        MyApp color    green      function bar        alert MyApp color      Alerts  green       No one should yell at you for doing something like the above

User · Answer

You can completely control the execution of javascript functions  and pass variables between them  using custom jQuery events    I was told that this wasn t possible all over these forums  but I got something working that does exactly that  even using an ajax call      Here s the answer  IMPORTANT  it s not the checked answer but rather the answer by me  Emile     How to get a variable returned across multiple functions - Javascript jQuery

User · Answer

I don t know specifics of your issue  but if the function needs the value then it can be a parameter passed through the call   Globals are considered bad because globals state and multiple modifiers can create hard to follow code and strange errors   To many actors fiddling with something can create chaos

User · Answer

If there s a chance that you will reuse this code  then I would probably make the effort to go with an object-oriented perspective   Using the global namespace can be dangerous -- you run the risk of hard to find bugs due to variable names that get reused   Typically I start by using an object-oriented approach for anything more than a simple callback so that I don t have to do the re-write thing  Any time that you have a group of related functions in javascript  I think  it s a candidate for an object-oriented approach

User · Answer

If another function needs to use a variable you pass it to the function as an argument   Also global variables are not inherently nasty and evil   As long as they are used properly there is no problem with them

User · Answer

To make a variable calculated in function A visible in function B  you have three choices    make it a global  make it an object property  or pass it as a parameter when calling B from A    If your program is fairly small then globals are not so bad   Otherwise I would consider using the third method   function A         var rand num   calculate random number        B rand num      function B r        use rand num r

User · Answer

Consider using namespaces    function         var local var    foo       global var    bar      this global var and window global var also work      function local function          global function   function               Both local function and global function have access to all local and global variables   Edit  Another common pattern   var ns    function            local stuff     function foo          function bar          function baz         this one stays invisible         stuff visible in namespace object     return           foo   foo          bar   bar                The returned properties can now be accessed via the namespace object  e g  ns foo  while still retaining access to local definitions

User · Answer

Consider using namespaces    function         var local var    foo       global var    bar      this global var and window global var also work      function local function          global function   function               Both local function and global function have access to all local and global variables   Edit  Another common pattern   var ns    function            local stuff     function foo          function bar          function baz         this one stays invisible         stuff visible in namespace object     return           foo   foo          bar   bar                The returned properties can now be accessed via the namespace object  e g  ns foo  while still retaining access to local definitions

User · Answer

I don t know specifics of your issue  but if the function needs the value then it can be a parameter passed through the call   Globals are considered bad because globals state and multiple modifiers can create hard to follow code and strange errors   To many actors fiddling with something can create chaos

User · Answer

I think your best bet here may be to define a single global-scoped variable  and dumping your variables there   var MyApp          Globally scoped object  function foo        MyApp color    green      function bar        alert MyApp color      Alerts  green       No one should yell at you for doing something like the above

[javascript] Accessing variables from other functions without using global variables

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