Checking for Undefined In React

Question

I have a scenario where I m passing data from a reducer into my react state    data          id   1       title    Test        content              body    sdfsdf           image    http   example com            Using componentWillRecieveProps  this works perfectly for retrieving the title   componentWillReceiveProps nextProps        this setState           title  nextProps blog title             However  I m having difficulty retrieving the nested fields  When I do this   componentWillReceiveProps nextProps        console log  new title is   nextProps blog title       console log  new body content is   nextProps blog content  body         this setState           title  nextProps blog title          body  nextProps blog content  body              I get this error      The error of an undefined body goes away after I click the debugger and the content is loaded  Is there anyway I can combat this issue    I tried to check for undefined like this   if  typeof nextProps blog content  body       undefined      But this doesn t work either and I believe it s because the blog is undefined

User · Answer

In case you also need to check if nextProps blog is not undefined   you can do that in a single if statement  like this  if  typeof nextProps blog      quot undefined quot   amp  amp  typeof nextProps blog content      quot undefined quot               And  when an undefined   empty or null value is not expected  you can make it more concise  if  nextProps blog  amp  amp  nextProps blog content

User · Answer

You can try adding a question mark as below  This worked for me   componentWillReceiveProps nextProps        this setState           title  nextProps  blog  title          body  nextProps  blog  content

User · Answer

You can check undefined object using below code      ReactObject      undefined

User · Answer

What you can do is check whether you props is defined initially or not by checking if nextProps blog content is undefined or not since your body is nested inside it like  componentWillReceiveProps nextProps         if nextProps blog content     undefined  amp  amp  nextProps blog title     undefined           console log  new title is   nextProps blog title          console log  new body content is   nextProps blog content  body            this setState              title  nextProps blog title             body  nextProps blog content  body                       You need not use type to check for undefined  just the strict operator     which compares the value by their type as well as value   In order to check for undefined  you can also use the typeof operator like  typeof nextProps blog content     undefined

User · Answer

I was face same problem       And I got solution by using typeof   if  typeof value       undefined   amp  amp  value    null             console log  Not Undefined and Not Null       else            console log  Undefined or Null      You must have to use typeof   to identified undefined

[reactjs] Checking for Undefined In React

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