Locate the function in your code that uses return codes to indicate success or failure. In our case, the function is divide.
Modify the function to throw an error when an invalid operation is detected. In our case, we throw an error when the parameter b is zero.
-
Set the error message to "Division by zero is not allowed".
+
Set the error message to "Division by zero is forbidden".
Update the success path to return the result of the division operation.
Modify the calling code to use a try block to wrap the call to the divide function.
Within the try block, log the result of the division operation if no error is thrown.
@@ -219,10 +70,10 @@
Interactive Lab ()
// Implement a simple division method that returns the result of a / b
function divide(a, b) {
if (b === 0) {
-
+
} else {
-
}
}
diff --git a/docs/labs/handling-errors.js b/docs/labs/handling-errors.js
new file mode 100644
index 00000000..1d656aba
--- /dev/null
+++ b/docs/labs/handling-errors.js
@@ -0,0 +1,167 @@
+info =
+{
+ hints: [
+ {
+ index: 0,
+ absent: "; $",
+ text: "This code uses the convention of terminating each line with a semicolon; please follow the conventions of the code being modified.\n"
+ },
+ {
+ index: 0,
+ present: "(Throw|THROW|New|NEW|error|ERROR)",
+ text: "JavaScript is case-sensitive. use throw new Error(...).",
+ examples: [
+ [ " Throw new Error(\"Division by zero is forbidden\");" ],
+ [ " THROW new Error(\"Division by zero is forbidden\");" ],
+ [ " throw New Error(\"Division by zero is forbidden\");" ],
+ [ " throw NEW Error(\"Division by zero is forbidden\");" ],
+ [ " throw new error(\"Division by zero is forbidden\");" ],
+ [ " throw new ERROR(\"Division by zero is forbidden\");" ]
+ ]
+ },
+ {
+ index: 0,
+ absent: "throw",
+ text: "Try using the throw keyword to raise an exception, E.g., throw new Error(\"Message\").",
+ examples: [
+ [ " return { success: false, message: \"Division by zero is forbidden\" };" ],
+ [ " return \"Division by zero is forbidden\" ;" ]
+ ]
+ },
+ {
+ index: 1,
+ absent: "return",
+ text: "Use the return keyword to return the result of the division.",
+ examples: [
+ [ " a / b ;" ]
+ ]
+ },
+ {
+ index: 1,
+ present: "{ (.*?)} ",
+ text: "Try simply returning the result of the division.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ " return { success: true, result: a / b };"
+ ],
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ " return { result: a / b };"
+ ]
+ ]
+ },
+ {
+ index: 2,
+ absent: String.raw`\s*try\s*{\s* `,
+ text: "Use a try block to catch any exceptions that might be thrown. It should look something like `try { ... } catch(err) {...}` (fill in the `...` sections).",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " const result = divide(10, 2);"
+ ]
+ ]
+ },
+ {
+ index: 2,
+ present: String.raw`\s* try \s* { .*? if \( result.success \) .*?`,
+ text: "You may assume that the result is successful within the try block.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); if( result.success) { console.log ( \"Result:\", result ); "
+ ]
+ ]
+ },
+ {
+ index: 2,
+ present: ".*? result.result .*?",
+ text: "The result is not an object, it is a number.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result.result ); "
+ ]
+ ]
+ },
+ {
+ index: 2,
+ absent: ".*? catch .*? ",
+ text: "Handle the error within the catch block. You need `catch(err) {...}` after `try {...}` to catch an error in the try block.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result ); }"
+ ]
+ ]
+ },
+ {
+ index: 2,
+ absent: String.raw`\s* catch \s* \( .*? \) { \s* `,
+ text: "Use 'catch (...) {...}' to catch an error object within the catch block.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result ); } catch {}"
+ ]
+ ]
+ },
+ {
+ index: 2,
+ absent: String.raw`catch \( err \)`,
+ text: "Please use `catch(err) {...}` for purposes of this lab.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result ); } catch (foo) {"
+ ]
+ ]
+ },
+ {
+ index: 2,
+ present: String.raw`catch .* console \. error \( ["'][^"']*["'] , result`,
+ text: "When reporting the error, you need to report it in the catch block, which catches it as the variable `err`. Thus, you need to use `err.message` not `result` or `result.message`, since the error is in `err.message`. Note that the variable `result` is out of scope in the catch block anyway; it was declared in the try block.",
+ examples: [
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result ); } catch (err) { console.error('Error', result.message);"
+ ],
+ [
+ "throw new Error(\"Division by zero is forbidden\");",
+ "return a / b;",
+ " try { const result = divide(10 ,2); console.log ( \"Result:\", result ); } catch (err) { console.error('Error', result );"
+ ]
+ ]
+ }
+ ],
+ expected: [
+ 'throw new Error("Division by zero is forbidden");',
+ 'return a / b;',
+`try {
+ const result = divide(10, 2);
+ console.log("Result:", result);
+} catch (err) {
+ console.error("Error:", err.message);
+}`
+ ],
+ correct: [
+ String.raw`\s* throw new Error \( ("(.*)"|'(.*)'|${BACKQUOTE}(.*)${BACKQUOTE}) \) ; \s*`,
+ String.raw`\s* return a \/ b ; \s*`,
+ String.raw`\s* try \{
+ const result = divide \( 10 , 2 \) ;
+ console \. log \(
+ ("Result:" | 'Result:' | ${BACKQUOTE}Result:${BACKQUOTE}) , result \) ;
+ \} catch \( err \) {
+ console.error \(
+ ("Error:" | 'Error:' | ${BACKQUOTE}Error:${BACKQUOTE}) ,
+ err \. message \) ;
+ \} \s*`
+ ],
+}