Implement program flow - Programming in HTML5 with JavaScript and CSS3 - page 151

Another part to the try…catch block is the finally. block. This block is added directly after
the catch block. The significance of the finally. block is that the code inside it runs all the time.
This isn't to say that the code in the finally. block can't have its own errors resulting in excep-
tions, but whether or not the code in the try block has an error, the code in the finally. block
still runs. Consider the following code:
function WorkthroughArray() {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
context.fillStyle = "blue";
contxt.arc(50, 50, 25, 0, 360);
context.fill();
context.strokeStyle = "red";
context.stroke();
}
This function contains an intentional spelling error, contxt, which results in an exception.
Nothing after the line that causes the exception runs. However, placing a try…catch…finally
block around this code provides more control over the flow:
try{
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
context.fillStyle = "blue";
contxt.arc(50, 50, 25, 0, 360);
context.fill();
context.strokeStyle = "red";
context.stroke();
}
catch (e) {
console.log(e.message);
}
finally {
//do any final logic before exiting the method
}
Now, with the structured error handling in place, when the line with the typo is hit,
processing jumps into the catch block. In this block, the error could be logged for future
diagnostics. After the catch block completes, the finally. block runs. If any cleanup or variable
resetting needs to be done, it can be done here even though an exception occurs. The finally.
block also runs. If the typo is fixed so that no exceptions occur in the try block, the catch
doesn't occur because of nothing to catch, but the finally. block still runs. The finally. block
always runs as the last part of a try…catch…finally block.
Variable scope applies to each block within the try…catch block. If a variable is declared
within the try portion, it won't be accessible from the catch of the finally. . If you want to have