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, , , . HttpError, DbError, NotFoundError .

, message, name , , stack. , , HttpError statusCode , - 404, 403 500.

JavaScript throw - , Error. , obj instanceof Error . .

, , . , HttpTimeoutError HttpError .

Error

, readUser(json), JSON .

, json:

let json = `{ "name": "", "age": 30 }`;

JSON.parse. json, SyntaxError. json , , , ? . , name age, .

readUser(json) JSON, () . , . SyntaxError, , . ValidationError . , .

ValidationError Error.

Error , , , :

          // ""    Error,   JavaScript
class Error {
  constructor(message) {
    this.message = message;
    this.name = "Error"; // (      )
    this.stack = <call stack>; //  ,     
  }
}
        

ValidationError :

class ValidationError extends Error {
  constructor(message) {
    super(message); // (1)
    this.name = "ValidationError"; // (2)
  }
}

function test() {
  throw new ValidationError("!");
}

try {
  test();
} catch(err) {
  alert(err.message); // !
  alert(err.name); // ValidationError
  alert(err.stack); //        
}

: (1) . JavaScript super , . message.

name "Error", (2) .

readUser(json):

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

// Usage
function readUser(json) {
  let user = JSON.parse(json);

  if (!user.age) {
    throw new ValidationError("No field: age");
  }
  if (!user.name) {
    throw new ValidationError("No field: name");
  }

  return user;
}

//    try..catch

try {
  let user = readUser('{ "age": 25 }');
} catch (err) {
  if (err instanceof ValidationError) {
    alert("Invalid data: " + err.message); // Invalid data: No field: name
  } else if (err instanceof SyntaxError) { // (*)
    alert("JSON Syntax Error: " + err.message);
  } else {
    throw err; //  ,    (**)
  }
}

try..catch ValidationError, SyntaxError JSON.parse.

, , instanceof (*).

err.name, :

          // ...
//  (err instanceof SyntaxError)
} else if (err.name == "SyntaxError") { // (*)
// ...
        

instanceof , ValidationError, , , PropertyRequiredError. instanceof . .

, catch , (**). catch , , ( ) .

ValidationError . . (, age ). PropertyRequiredError, . , .

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

class PropertyRequiredError extends ValidationError {
  constructor(property) {
    super("No property: " + property);
    this.name = "PropertyRequiredError";
    this.property = property;
  }
}

// Usage
function readUser(json) {
  let user = JSON.parse(json);

  if (!user.age) {
    throw new PropertyRequiredError("age");
  }
  if (!user.name) {
    throw new PropertyRequiredError("name");
  }

  return user;
}

//    try..catch

try {
  let user = readUser('{ "age": 25 }');
} catch (err) {
  if (err instanceof ValidationError) {
    alert("Invalid data: " + err.message); // Invalid data: No property: name
    alert(err.name); // PropertyRequiredError
    alert(err.property); // name
  } else if (err instanceof SyntaxError) {
    alert("JSON Syntax Error: " + err.message);
  } else {
    throw err; //  ,  
  }
}

PropertyRequiredError : : new PropertyRequiredError(property). message .

, this.name PropertyRequiredError . this.name = < > . , , this.name = this.constructor.name. .

MyError.

MyError :

class MyError extends Error {
  constructor(message) {
    super(message);
    this.name = this.constructor.name;
  }
}

class ValidationError extends MyError { }

class PropertyRequiredError extends ValidationError {
  constructor(property) {
    super("No property: " + property);
    this.property = property;
  }
}

//  name
alert( new PropertyRequiredError("field").name ); // PropertyRequiredError

, ValidationError, "this.name = ..." .

readUser . . SyntaxError ValidationError, readUser , , .

, readUser, . if catch, , .

          try {
  ...
  readUser()  //   
  ...
} catch (err) {
  if (err instanceof ValidationError) {
    //    
  } else if (err instanceof SyntaxError) {
    //   
  } else {
    throw err; //  ,  
  }
}
        

, .

readUser , : ?

: . , , ( ). , , , .

, , .

ReadError, .
readUser , , , ValidationError SyntaxError, ReadError.
ReadError cause.

, readUser, ReadError, . , cause.

, ReadError readUser try..catch:

class ReadError extends Error {
  constructor(message, cause) {
    super(message);
    this.cause = cause;
    this.name = 'ReadError';
  }
}

class ValidationError extends Error { /*...*/ }
class PropertyRequiredError extends ValidationError { /* ... */ }

function validateUser(user) {
  if (!user.age) {
    throw new PropertyRequiredError("age");
  }

  if (!user.name) {
    throw new PropertyRequiredError("name");
  }
}

function readUser(json) {
  let user;

  try {
    user = JSON.parse(json);
  } catch (err) {
    if (err instanceof SyntaxError) {
      throw new ReadError("Syntax Error", err);
    } else {
      throw err;
    }
  }

  try {
    validateUser(user);
  } catch (err) {
    if (err instanceof ValidationError) {
      throw new ReadError("Validation Error", err);
    } else {
      throw err;
    }
  }

}

try {
  readUser('{bad json}');
} catch (e) {
  if (e instanceof ReadError) {
    alert(e);
    // Original error: SyntaxError: Unexpected token b in JSON at position 1
    alert("Original error: " + e.cause);
  } else {
    throw e;
  }
}

readUser , ReadError ( , ).

, instanceof ReadError . .

, ReadError, . - .

Error . name super.
instanceof . . , , . name.
: . , , err.cause, , .

SyntaxError

FormatError, SyntaxError.

message, name stack.

          let err = new FormatError("formatting error");

alert( err.message ); // formatting error
alert( err.name ); // FormatError
alert( err.stack ); // stack

alert( err instanceof FormatError ); // true
alert( err instanceof SyntaxError ); // true (   SyntaxError)
        

class FormatError extends SyntaxError {
  constructor(message) {
    super(message);
    this.name = this.constructor.name;
  }
}

let err = new FormatError("formatting error");

alert( err.message ); // formatting error
alert( err.name ); // FormatError
alert( err.stack ); // stack

alert( err instanceof SyntaxError ); // true

, Error

Error

SyntaxError