How can a Javascript object refer to values in itself

Question

Lets say I have the following javascript   var obj      key1    it     key2   key1     works      alert obj key2     This errors with  key1 is not defined   I have tried   this key1 this key1  obj key1 obj key1  this  key1   obj  key1     and they never seem to be defined   How can I get key2 to refer to key1 s value

User · Answer

You can t refer to a property of an object before you have initialized that object  use an external variable   var key1    it   var obj       key1   key1    key2   key1     works        Also  this is not a  JSON object   it is a Javascript object  JSON is a method of representing an object with a string  which happens to be valid Javascript code

User · Answer

You can also reference the obj once you are inside the function instead of this   var obj         key1   it       key2  function   return obj key1     works       alert obj key2

User · Answer

This is not JSON  JSON was designed to be simple  allowing arbitrary expressions is not simple   In full JavaScript  I don t think you can do this directly  You cannot refer to this until the object called obj is fully constructed  So you need a workaround  that someone with more JavaScript-fu than I will provide

User · Answer

One alternative would be to use a getter setter methods   For instance  if you only care about reading the calculated value   var book        Object defineProperties book       key1    value   it   enumerable  true        key2            enumerable  true          get  function                return this key1     works                         console log book key2     prints  it works     The above code  though  won t let you define another value for key2    So  the things become a bit more complicated if you would like to also redefine the value of key2  It will always be a calculated value  Most likely that s what you want   However  if you would like to be able to redefine the value of key2  then you will need a place to cache its value independently of the calculation   Somewhat like this   var book       key2    works      Object defineProperties book       key1    value   it   enumerable  true        key2    enumerable  false       key2            enumerable  true          get  function                return this key1   this  key2                     set  function newValue               this  key2   newValue                       console log book key2     it works   book key2     doesn t work    console log book key2     it doesn t work   for var key in book         prints both key1 and key2  but not  key2     console log key         book key         Another interesting alternative is to use a self-initializing object   var obj        x   it     init  function        this y   this x     works        return this         init     console log obj y     it works

User · Answer

That s not a JSON object  that s a Javascript object created via object literal notation   JSON is a textual notation for data exchange  more   If you re dealing with JavaScript source code  and not dealing with a string  you re not dealing with JSON    There s no way within the object initializer to refer to another key of the object being initialized  because there s no way to get a reference to the object being created until the initializer is finished   There s no keyword akin to this or something for this situation

User · Answer

This can be achieved by using constructor function instead of literal  var o   new function       this foo    it     this bar   this foo     works     alert o bar

User · Answer

Because the statement defining obj hasn t finished  key1 doesn t exist yet  Consider this solution   var obj     key1   it     obj key2   obj key1          works       obj key2 is now  it works

User · Answer

Maybe you can think about removing the attribute to a function  I mean something like this    x000D   x000D  var obj     x000D    key1   it    x000D    key2  function     x000D      return this key1     works    x000D      x000D     x000D   x000D  alert obj key2     x000D   x000D   x000D

[javascript] How can a Javascript object refer to values in itself?

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