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。
語法
new Error([message[, fileName[, lineNumber]]])
參數
message
選擇性-
人們可閱讀的錯誤說明。
fileName
選擇性 非標準-
The value for the
fileName
property on the createdError
object. Defaults to the name of the file containing the code that called theError()
constructor. lineNumber
選擇性 非標準-
Optional. The value for the
lineNumber
property on the createdError
object. Defaults to the line number containing theError()
constructor invocation.
描述
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).
錯誤類型
Besides the generic Error
constructor, there are six other core error constructors in JavaScript. For client-side exceptions, see Exception Handling Statements (en-US).
EvalError
(en-US)-
Creates an instance representing an error that occurs regarding the global function
eval()
(en-US). InternalError
(en-US) 非標準-
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
(en-US)-
Creates an instance representing an error that occurs when de-referencing an invalid reference.
SyntaxError
(en-US)-
Creates an instance representing a syntax error that occurs while parsing code in
eval()
(en-US). TypeError
(en-US)-
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) ordecodeURI()
(en-US) are passed invalid parameters.
屬性
Error.prototype
(en-US)-
Allows the addition of properties to
Error
instances.
方法
The global Error
object contains no methods of its own, however, it does inherit some methods through the prototype chain.
Error
實體
Runtime errors result in new Error
objects being created and thrown.
Error
is a serializable object (en-US), so it can be cloned with structuredClone()
(en-US) or copied between Workers (en-US) using postMessage()
(en-US).
屬性
Error.prototype.message
(en-US)-
Error message. For user-created
Error
objects, this is the string provided as the constructor's first argument. Error.prototype.name
(en-US)-
Error name. This is determined by the constructor function.
Error.prototype.cause
(en-US)-
Error cause indicating the reason why the current error is thrown — usually another caught error. For user-created
Error
objects, this is the value provided as thecause
property of the constructor's second argument. Error.prototype.fileName
(en-US) 非標準-
A non-standard Mozilla property for the path to the file that raised this error.
Error.prototype.lineNumber
(en-US) 非標準-
A non-standard Mozilla property for the line number in the file that raised this error.
Error.prototype.columnNumber
非標準-
A non-standard Mozilla property for the column number in the line that raised this error.
Error.prototype.stack
(en-US) 非標準-
A non-standard property for a stack trace.
方法
Error.prototype.toString()
(en-US)-
Returns a string representing the specified object. Overrides the
Object.prototype.toString()
(en-US) method.
範例
Throwing a generic error
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
construct:
try {
throw new Error('Whoops!');
} catch (e) {
console.log(e.name + ': ' + e.message);
}
Handling a specific error
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
}
Custom Error Types
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.
警告: Note that the thrown MyError
will report incorrect lineNumber
and fileName
at least in Firefox.
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'
}
規範
Specification |
---|
ECMAScript Language Specification # sec-error-objects |
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