How to resolve TypeError Cannot convert undefined or null to object

Question

I ve written a couple of functions that effectively replicate JSON stringify    converting a range of values into stringified versions  When I port my code over to JSBin and run it on some sample values  it functions just fine  But I m getting this error in a spec runner designed to test this   My code        five lines of comments   var stringify   function obj      if  typeof obj      function     return undefined       return undefined for function   if  typeof obj      undefined     return undefined      return undefined for undefined   if  typeof obj      number     return obj      number unchanged   if  obj      null     return null      null unchanged   if  typeof obj      boolean     return obj      boolean unchanged   if  typeof obj      string     return        obj             string gets escaped end-quotes   if  Array isArray obj          return obj map function  e        uses map   to create new array with stringified elements         return stringify e               else       var keys   Object keys obj        convert object s keys into an array     var container   keys map function  k        uses map   to create an array of key  stringified value pairs         return k          stringify obj k                return       container join                 returns assembled object with curly brackets         var stringifyJSON   function obj        if  typeof stringify obj      undefined             return      stringify obj                   The error message I m getting from the tester is   TypeError  Cannot convert undefined or null to object     at Function keys  native      at stringify  stringifyJSON js 18 22      at stringifyJSON  stringifyJSON js 27 13      at stringifyJSONSpec js 7 20     at Array forEach  native      at Context  lt anonymous gt   stringifyJSONSpec js 5 26      at Test Runnable run  mocha js 4039 32      at Runner runTest  mocha js 4404 10      at mocha js 4450 12     at next  mocha js 4330 14    It seems to fail with  stringifyJSON null  for example

User · Answer

Replace if  typeof obj      undefined     return undefined      return undefined for undefined if  obj      null     return null      null unchanged  with if  obj     undefined    return undefined      return undefined for undefined  if  obj     null    return null      null unchanged

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In my case  I added Lucid extension to Chrome and didn t notice the problem at that moment  After about a day of working on the problem and turning the program upside down  in a post someone had mentioned Lucid  I remembered what I had done and removed the extension from Chrome and ran the program again  The problem was gone  I am working with React  I thought this might help

User · Answer

Make sure that destination object is not empty   null or undefined     You can initialize destination object with empty object like below   var destinationObj        Object assign destinationObj  sourceObj

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Below snippet is sufficient to understand how I encountered the same issue but in a different scenario and how I solved it using the guidance in the accepted answer  In my case I was trying to log the keys of object present in the 0th index of the  defaultViewData  array using Object keys   method  defaultViewData      quot name quot    quot DEFAULT VIEW PLP quot   quot value quot     quot MSH25 quot    quot LIST quot       console log  DEFAULT VIEW   Object keys this props defaultViewData 0      The console log was not getting printed and I was getting the same error as posted in this question  To prevent that error I added below condition     if this props defaultViewData 0       console log  DEFAULT VIEW   Object keys this props defaultViewData 0        Adding this check ensured that I didn t get this error  I hope this helps for someone  Note  This is React js code   although to understand the problem it doesn t matter

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If you re using Laravel  my problem was in the name of my Route  Instead  Route  put   reason update    REASONController update     I wrote  Route  put   reason update    RESONController update     and when I fixed the controller name  the code worked

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I solved the same problem in a React Native project  I solved it using this   let data   snapshot val    if data     let items   Object values data     else      return null

User · Answer

Generic answer  This error is caused when you call a function that expects an Object as its argument  but pass undefined or null instead  like for example  Object keys null  Object assign window UndefinedVariable        As that is usually by mistake  the solution is to check your code and fix the null undefined condition so that the function either gets a proper Object  or does not get called at all   Object keys   key    value    if  window UndefinedVariable        Object assign window UndefinedVariable          Answer specific to the code in question  The line if  obj      null     return null      null unchanged  will not  evaluate when given null  only if given the string  null   So if you pass the actual null value to your script  it will be parsed in the Object part of the code  And Object keys null  throws the TypeError mentioned  To fix it  use if obj     null   return null  - without the qoutes around null

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This is very useful to avoid errors when accessing properties of null or undefined objects  null to undefined object const obj   null  const newObj   obj    undefined     newObj   undefined  undefined to empty object const obj   const newObj   obj           newObj              newObj prop   undefined  but no error here  null to empty object const obj   null  const newObj   obj           newObj           newObj prop   undefined  but no error here

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I have the same problem with a element in a webform  So what I did to fix it was validate  if Object      null        do something

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In my case I had an extra pair of parenthesis    Instead of export default connect    someVariable   otherVariable     It had to be export default connect    someVariable   otherVariable

[javascript] How to resolve TypeError: Cannot convert undefined or null to object

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