JavaScript - cannot set property of undefined

Question

My code   var a    1   b    hello   c      100     some important data     d        d a   greeting     b  d a   data     c   console debug  d     I get the following error       Uncaught TypeError  Cannot set property  greeting  of undefined    I m trying to do something similar to an associative array  Why isn t this working

User · Answer

i d just do a simple check to see if d a  exists and if not initialize it     var a    1       b    hello       c      100     some important data         d            if  d a      undefined            d a                  d a   greeting     b      d a   data     c       console debug  d

User · Answer

d      is an empty object right now  And d a  is also an empty object   It does not have any key values  So you should initialize the key values to this  d a      greetings     data

User · Answer

In javascript almost everything is an object  null and undefined are exception   Instances of Array is an object  so you can set property of an array  for the same reason you can t set property of a undefined  because its NOT an object

User · Answer

The object stored at d a  has not been set to anything   Thus  d a  evaluates to undefined   You can t assign a property to undefined      You need to assign an object or array to d a    d a        d a   greeting     b   console debug d

User · Answer

You have to set d a  to either an associative array  or an object    d a        d a            Without setting  this is what s happening   d a     undefined  so you re doing undefined  greeting   b  and by definition  undefined has no properties   Thus  the error you received

User · Answer

you never set d a  to any value   Because of this  d a  evaluates to undefined  and you can t set properties on undefined   If you add d a       right after d      things should work as expected   Alternatively  you could use an object initializer   d a          greetings  b      data  c      Or you could set all the properties of d in an anonymous function instance   d   new function          this a              greetings  b          data  c               If you re in an environment that supports ES2015 features  you can use computed property names   d        a         greetings  b      data  c

[javascript] JavaScript - cannot set property of undefined

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