try { //statements that may cause an error } catch (err) { //err holds info about the error //statements that handle an error, if one happens throw err //if you decide to error after all } finally { //optional //statements that happen error or not }
There are 3 types of errors:
#1 is corrected by the programmer learning and fixing the code. #2 can be fixed by adding more code to better check the data, but it starts to get annoying... #3 can't be fixed... except by a try-catch block. And, they really manes dealing with bad data easy. Just don't deal with it, and reject anything that causes a crash.
The catch block can example the error object and take action based on the type of the error. e.g.
try { something(); } catch (e) { if (e instanceof RangeError) { // statements to handle this very common expected error console.log("out of range"+e) throw "value out of range" } else { throw e; // re-throw the error unchanged } }
The error object also has two attributes: .name which is the general class of error, and .message which is a short error message.
Error classes include:
The throw keyword accepts any expression, or can be used with new to make a new error object of any error class or a generic error. E.g.
throw "bogus" //directly using a string or other value throw my_error_messages(32) //function can return a value for the error throw new Error("bogus") //generic error with message throw new TypeError("value must be a widget") //error of type TypeError
See also:
file: /Techref/language/JAVA/SCRIPT/try-catch-finally.htm, 2KB, , updated: 2020/3/1 22:27, local time: 2024/12/23 06:29,
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