JavaScript provides an exception handling mechanism. Exceptions are unusual (but not completely unexpected) mishaps that interfere with the normal flow of a program. When such a mishap is detected, your program should throw an exception:
var add = function (a, b) { if (typeof a !== 'number' || typeof b !== 'number') { throw { name: 'TypeError', message: 'add needs numbers' }; } return a + b; }
The throw
statement interrupts execution of the
function. It should be given an exception
object
containing a name
property that identifies the
type of the exception, and a descriptive message
property. You can also add other properties.
The exception
object will be delivered to the
catch
clause of a try
statement:
// Make a try_it function that calls the new add // function incorrectly. var try_it = function ( ) { try { add("seven"); } catch (e) { document.writeln(e.name + ': ' + e.message); } } try_it( );
If an exception is thrown within a try
block,
control will go to its catch
clause.
A try
statement has a single catch
block that will catch all exceptions. If your
handling depends on the type of the exception, then the exception handler will have
to inspect the name
to determine the type of the
exception.
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