The try implements error handling for JavaScript.
The try...catch statement provides a way to handle some or all of the possible errors that may occur in a given block of code, while still running code. If errors occur that the programmer has not handled, JavaScript simply provides its normal error message to a user, as if there was no error handling.
The tryStatement argument contains code where an error can occur, while catchStatement contains the code to handle any error that does occur. If an error occurs in the tryStatement, program control is passed to catchStatement for disposition. The initial value of exception is the value of the error that occurred in tryStatement.
If the error cannot be handled in the catchStatement associated with the tryStatement where the error occurred, use the throw statement to propagate, or rethrow, the error to a higher-level error handler.
The following example throws an error based on a passed-in value. It then illustrates how that error is handled in a hierarchy of try...catch statements:
function TryCatchDemo(x)
{
try {
try {
if (x == 0) // Evalute argument.
throw "x equals zero"; // Throw an error.
else
throw "x does not equal zero"; // Throw a different error.
}
catch(e) { // Handle "x = 0" errors here.
if (e == "x equals zero") // Check for an error handled here.
return(e + " handled locally."); // Return object error message.
else // Can't handle error here.
throw e; // Rethrow the error for next
} // error handler.
}
catch(e) { // Handle other errors here.
return(e + " handled higher up."); // Return error message.
}
}
document.write(TryCatchDemo(0));
document.write(TryCatchDemo(1));
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To run the code, paste it into 