Error

Error 建構函式能用來建立一個 error 物件。當執行期間發生錯誤時，Error 物件實體會被拋出。Error 物件也可作為自訂例外的基礎物件，請參考下方的標準內建錯誤類型。

new Error([message[, fileName[, lineNumber]]])

message 選擇性

人們可閱讀的錯誤說明。

fileName 選擇性

The value for the fileName property on the created Error object. Defaults to the name of the file containing the code that called the Error() constructor.

lineNumber 選擇性

Optional. The value for the lineNumber property on the created Error object. Defaults to the line number containing the Error() constructor invocation.

Runtime errors result in new Error objects being created and thrown.

This page documents the use of the Error object itself and its use as a constructor function. For a list of properties and methods inherited by Error instances, see Error.prototype (en-US).

Besides the generic Error constructor, there are six other core error constructors in JavaScript. For client-side exceptions, see Exception Handling Statements.

EvalError

Creates an instance representing an error that occurs regarding the global function eval() (en-US).

InternalError

Creates an instance representing an error that occurs when an internal error in the JavaScript engine is thrown. E.g. "too much recursion".

RangeError

Creates an instance representing an error that occurs when a numeric variable or parameter is outside of its valid range.

ReferenceError

Creates an instance representing an error that occurs when de-referencing an invalid reference.

SyntaxError

Creates an instance representing a syntax error that occurs while parsing code in eval() (en-US).

TypeError

Creates an instance representing an error that occurs when a variable or parameter is not of a valid type.

URIError

Creates an instance representing an error that occurs when encodeURI() (en-US) or decodeURI() (en-US) are passed invalid parameters.

Error.prototype (en-US)

Allows the addition of properties to Error instances.

The global Error object contains no methods of its own, however, it does inherit some methods through the prototype chain.

Usually you create an Error object with the intention of raising it using the throw keyword. You can handle the error using the try...catch (en-US) construct:

try {
  throw new Error('Whoops!');
} catch (e) {
  console.log(e.name + ': ' + e.message);
}

You can choose to handle only specific error types by testing the error type with the error's constructor (en-US) property or, if you're writing for modern JavaScript engines, instanceof (en-US) keyword:

try {
  foo.bar();
} catch (e) {
  if (e instanceof EvalError) {
    console.log(e.name + ': ' + e.message);
  } else if (e instanceof RangeError) {
    console.log(e.name + ': ' + e.message);
  }
  // ... etc
}

You might want to define your own error types deriving from Error to be able to throw new MyError() and use instanceof MyError to check the kind of error in the exception handler. The common way to do this is demonstrated below.

See also the "What's a good way to extend Error in JavaScript?" discussion on Stackoverflow.

// Create a new object, that prototypically inherits from the Error constructor
function MyError(message) {
  this.name = 'MyError';
  this.message = message || 'Default Message';
  this.stack = (new Error()).stack;
}
MyError.prototype = Object.create(Error.prototype);
MyError.prototype.constructor = MyError;

try {
  throw new MyError();
} catch (e) {
  console.log(e.name);     // 'MyError'
  console.log(e.message);  // 'Default Message'
}

try {
  throw new MyError('custom message');
} catch (e) {
  console.log(e.name);     // 'MyError'
  console.log(e.message);  // 'custom message'
}

• Error.prototype (en-US)
• throw
• try...catch (en-US)