Javascript Not a Constructor Exception while creating objects

Question

I am defining an object like this   function Project Attributes  ProjectWidth  ProjectHeight        this ProjectHeight   ProjectHeight      this ProjectWidth   ProjectWidth      this ProjectScale   this GetProjectScale        this Attributes   Attributes       this currentLayout            this CreateLayoutArray   function                  I then try to create and instance like this   var newProj   new Project a b c     But this execption is thrown   Project is not a constructor   What could be wrong  I googled around a lot  but still can t figure out what I am doing wrong

User · Answer

In my case I d forgotten the open and close parantheses at the end of the definition of the function wrapping all of my code in the exported module  I e  I had    function         use strict      module exports MyClass   class             Instead of    function         use strict      module exports MyClass   class               The compiler doesn t complain  but the require statement in the importing module doesn t set the variable it s being assigned to  so it s undefined at the point you try to construct it and it will give the TypeError  MyClass is not a constructor error

User · Answer

I ve googled around also and found this solution   You have a variable Project somewhere that is not a function  Then the new operator will complain about it  Try console log Project  at the place where you would have used it as a construcotr  and you will find it

User · Answer

I had a similar error and my problem was that the name and case of the variable name and constructor name were identical  which doesn t work since javascript interprets the intended constructor as the newly created variable   In other words   function project name       this name   name       elsewhere       this is no good  name case are identical so javascript barfs   let project   new project  My Project      Simply changing case or variable name fixes the problem  though     with a capital  P  function Project name       this name   name       elsewhere       works  class name case is dissimilar to variable name let project   new Project  My Project

User · Answer

To add to  wprl s answer  the ES6 object method shorthand  like the arrow functions  cannot be used as a constructor either    const o       a       gt        b         c  function           const   a  b  c     o   new a       throws  a is not a constructor  new b       throws  b is not a constructor  new c       works

User · Answer

In my case I was using the prototype name as the object name  For e g   function proto1       var proto1   new proto1      It was a silly mistake but might be of help to someone like me

User · Answer

It is happening because you must have used another variable named  project  in your code  Something like  var project       For you to make the code work  change as follows   var project      into var project1

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Car js  class Car    getName    return  car      export default Car    TestFile js  const object   require    Car js    const instance   new object      error  TypeError  instance is not a constructor  printing content of object  object    default  Car    append default to the require function and it will work as contructor  const object   require  object-fit-images   default  const instance   new object    instance getName

User · Answer

For me it was the differences between import and require on ES6    E g      processor js class Processor       export default Processor    index js const Processor   require    processor    const processor   new Processor     fails with the error  import Processor from    processor  const processor   new Processor      succeeds

User · Answer

For my project  the problem turned out to be a circular reference created by the require   calls   y js  var x   require    x js    var y   function     console log  result is     x      module exports   y   x js  var y   require    y js    var my y   new y        lt - TypeError  y is not a constructor var x   function     console log  result is     my y    module exports   x    The reason is that when it is attempting to initialize y  it creates a temporary  y  object  not class  object   in the dependency system that is somehow not yet a constructor  Then  when x js is finished being defined  it can continue making y a constructor  Only  x js has an error in it where it tries to use the non-constructor y

User · Answer

To add the solution I found to this problem when I had it  I was including a class from another file and the file I tried to instantiate it in gave the  quot not a constructor quot  error   Ultimately the issue was a couple unused requires in the other file before the class was defined   I m not sure why they broke it  but removing them fixed it   Always be sure to check if something might be hiding in between the steps you re thinking about

User · Answer

I have a class in one file that I m importing into a test file     Vec js class Vec       module exports Vec   Vec    Changing     Vec test js const Vec   require    Vec    const myVec   new Vec      TypeError  Vec is not a constructor   to     Vec test js const  Vec    require    Vec    const myVec   new Vec      Succeeds    resolved this error for me

User · Answer

I just want to add that if the constructor is called from a different file  then something as simple as forgetting to export the constructor with  module exports   NAME OF CONSTRUCTOR   will also cause the  Not a constructor  exception

User · Answer

Sometimes it is just how you export and import it  For this error message it could be  that the default keyword is missing   export default SampleClass      Where you instantiate it   import SampleClass from  path to class   let sampleClass   new SampleClass      Option 2  with curly braces   export SampleClass    import   SampleClass   from  path to class   let sampleClass   new SampleClass

User · Answer

An additional cause of this can be ES2015 arrow functions   They cannot be used as constructors     const f        gt      new f       This throws  f is not a constructor

User · Answer

The code as posted in the question cannot generate that error  because Project is not a user-defined function   valid constructor   function x a b c    new x 1 2 3                    produces no errors   You ve probably done something like this   function Project a b c     Project                        or possibly   Project   new Project new Project 1 2 3              - gt  TypeError  Project is not a constructor   Variable declarations using var are hoisted and thus always evaluated before the rest of the code  So  this can also be causing issues   function Project     function localTest         new Project 1 2 3       Project  points to the local variable                             not the global constructor           some noise  causing you to forget that the  Project  constructor was used     var Project   1        Evaluated first

[javascript] Javascript "Not a Constructor" Exception while creating objects

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