Error() constructor
The Error()
constructor creates Error
objects.
Syntax
new Error()
new Error(message)
new Error(message, options)
new Error(message, fileName)
new Error(message, fileName, lineNumber)
Error()
Error(message)
Error(message, options)
Error(message, fileName)
Error(message, fileName, lineNumber)
Note: Error()
can be called with or without new
. Both create a new Error
instance.
Parameters
message
Optional-
A human-readable description of the error.
options
Optional-
An object that has the following properties:
fileName
Optional Non-standard-
The path to the file that raised this error, reflected in the
fileName
property. Defaults to the name of the file containing the code that called theError()
constructor. lineNumber
Optional Non-standard-
The line number within the file on which the error was raised, reflected in the
lineNumber
property. Defaults to the line number containing theError()
constructor invocation.
Examples
Function call or new construction
When Error
is used like a function, that is without new
, it will return an Error
object.
Therefore, a mere call to Error
will produce the same output that constructing an Error
object via the new
keyword would.
const x = Error("I was created using a function call!");
// above has the same functionality as following
const y = new Error('I was constructed via the "new" keyword!');
Rethrowing an error with a cause
It is sometimes useful to catch an error and re-throw it with a new message.
In this case you should pass the original error into the constructor for the new Error
, as shown.
try {
frameworkThatCanThrow();
} catch (err) {
throw new Error("New error message", { cause: err });
}
For a more detailed example see Error > Differentiate between similar errors.
Omitting options argument
JavaScript only tries to read options.cause
if options
is an object — this avoids ambiguity with the other non-standard Error(message, fileName, lineNumber)
signature, which requires the second parameter to be a string. If you omit options
, pass a primitive value as options
, or pass an object without the cause
property, then the created Error
object will have no cause
property.
// Omitting options
const error1 = new Error("Error message");
console.log("cause" in error1); // false
// Passing a primitive value
const error2 = new Error("Error message", "");
console.log("cause" in error2); // false
// Passing an object without a cause property
const error3 = new Error("Error message", { details: "http error" });
console.log("cause" in error3); // false
Specifications
Specification |
---|
ECMAScript Language Specification # sec-error-constructor |
Browser compatibility
BCD tables only load in the browser
See also
- Polyfill of
Error
withcause
support incore-js
throw
try...catch
- Error causes on v8.dev (2021)