What is the difference between throw new Error and throw someObject

Question

I want to write a common error handler which will catch custom errors thrown on purpose at any instance of the code   When I did throw new Error  sample   like in the following code  try       throw new Error   hehe   haha            throw new Error  hehe      catch e        alert e       console log e       Log shows in Firefox as Error   object Object  and I couldn   t parse the object   For the second throw the log shows as  Error  hehe  Whereas when I did  try       throw    hehe   haha       catch e        alert e       console log e       the console showed as  Object   hehe  haha   in which I was able to access the error properties   What is the difference   Is the difference as seen in the code  Like string will be just passed as string and object as objects but the syntax will be different   I haven   t explored throwing error object    I had done only throwing strings   Is there any other way than the above two mentioned methods

User · Accepted Answer

The difference between  throw new Error  and  throw someObject  in javascript is that throw new Error wraps the error passed to it in the following format -       name   Error      message   String you pass in the constructor     The throw someObject will throw the object as is and will not allow any further code execution from the try block  ie same as throw new Error  Here is a good explanation about The Error object and throwing your own errors The Error Object Just what we can extract from it in an event of an error  The Error object in all browsers support the following two properties   name  The name of the error  or more specifically  the name of the constructor function the error belongs to   message  A description of the error  with this description varying depending on the browser    Six possible values can be returned by the name property  which as mentioned correspond to the names of the error s constructors  They are  Error Name          Description  EvalError           An error in the eval   function has occurred   RangeError          Out of range number value has occurred   ReferenceError      An illegal reference has occurred   SyntaxError         A syntax error within code inside the eval   function has occurred                      All other syntax errors are not caught by try catch finally  and will                     trigger the default browser error message associated with the error                       To catch actual syntax errors  you may use the onerror event   TypeError           An error in the expected variable type has occurred   URIError            An error when encoding or decoding the URI has occurred                      ie  when calling encodeURI      Throwing your own errors  exceptions  Instead of waiting for one of the 6 types of errors to occur before control is automatically transferred from the try block to the catch block  you can also explicitly throw your own exceptions to force that to happen on demand  This is great for creating your own definitions of what an error is and when control should be transferred to catch

User · Answer

You first mention this code  throw new Error  sample    and then in your first example you write  throw new Error   hehe   haha      The first Error object would actually be useful  because it is expecting a string value  in this case  sample   The second would not because you are trying to pass an object in  and it is expecting a string  and would not display a helpful error  The error object would have the  quot message quot  property  which would be  sample

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The following article perhaps goes into some more detail as to which is a better choice  throw  An error  or throw new Error  An error     http   www nczonline net blog 2009 03 10 the-art-of-throwing-javascript-errors-part-2   It suggests that the latter  new Error    is more reliable  since browsers like Internet Explorer and Safari  unsure of versions  don t correctly report the message when using the former      Doing so will cause an error to be thrown  but not all browsers respond the way you   d expect  Firefox  Opera  and Chrome each display an    uncaught exception    message and then include the message string  Safari and Internet Explorer simply throw an    uncaught exception    error and don   t provide the message string at all  Clearly  this is suboptimal from a debugging point of view

User · Answer

React behavior Apart from the rest of the answers  I would like to show one difference in React  If I throw a new Error   and I am in development mode  I will get an error screen and a console log  If I throw a string literal  I will only see it in the console and possibly miss it  if I am not watching the console log  Example Throwing an error logs into the console and shows an error screen while in development mode  the screen won t be visible in production   throw new Error  quot The application could not authenticate  quot      Whereas the following code only logs into the console  throw  quot The application could not authenticate  quot

User · Answer

throw something works with both object and strings But it is less supported than the other method throw new Error  quot  quot    Will only work with strings and turns objects into useless  Object obj  in the catch block

User · Answer

The Error constructor is used to create an error object  Error objects are thrown when runtime errors occur  The Error object can also be used as a base object for user-defined exceptions    User-defined Errors are thrown via the throw statement  program control will be passed to the first catch block in the call stack   The difference between throwing an error with and without Error object     throw   hehe   haha      In chrome devtools looks like this     Chrome tells us that we have an uncaught error which just is a JS object  The object itself could have information regarding the error but we still don t know immediately where it came from  Not very useful when we are working on our code and debugging it     throw new Error   hehe   haha        In chrome devtools looks like this     An error thrown with the Error object gives us a stack trace when we expand it  This gives us valuable information where the error precisely came from which is often valuable information when debugging your code  Further note that the error says   object Object   this is because the Error constructor expects a message string as a first argument  When it receives a object it will coerce it into a string

User · Answer

TLDR  they are equivalent Error x      new Error x      this  const x   Error  I was created using a function call            has the same functionality as this  const y   new Error  I was constructed via the  quot new quot  keyword      source  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Error throw and throw Error will are functionally equivalent  But when you catch them and serialize them to console log they are not serialized exactly the same way  throw  Parameter is not a number    throw new Error  Parameter is not a number     throw Error  Parameter is not a number      Console log e  of the above will produce 2 different results  Parameter is not a number  Error  Parameter is not a number  Error  Parameter is not a number

User · Answer

you can throw as object  throw   message   This Failed      then for example in your try catch  try        catch e        console log e      message   This Failed       console log e message     This Failed     or just throw a string error  throw   Your error    try        catch e        console log e     Your error    throw new Error   only accept a string

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throw  quot I m Evil quot  throw will terminate the further execution  amp  expose message string on  catch the error   x000D   x000D  try     throw  I m Evil    console log  You ll never reach to me   123465    catch  e      console log e      I m Evil   x000D   x000D   x000D   Console after throw will never be reached cause of termination   throw new Error  quot I m Evil quot   throw new Error exposes an error event with two params name  amp  message  It also terminate further execution  x000D   x000D  try     throw new Error  I m Evil     console log  You ll never reach to me   123465    catch  e      console log e name  e message      Error I m Evil   x000D   x000D   x000D   throw Error  quot I m Evil quot   And just for completeness  this works also  though is not technically the correct way to do it -  x000D   x000D  try     throw Error  I m Evil     console log  You ll never reach to me   123465    catch  e      console log e name  e message      Error I m Evil    console log typeof new Error  hello        object console log typeof Error      function x000D   x000D   x000D

[javascript] What is the difference between `throw new Error` and `throw someObject`?

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