Debugging and Error Handling

Question 1

8 types of errors

Answer 1

Error: runtime error
ReferenceError
SyntaxError
TypeError - invalid type, can’t be used there
EvalError - when using eval()
InternalError - represents an internal error in the JS engine; for e.g. excessive recursion
RangeError - numeric variable outside of its valid range
URIError - error when encoding or decoding an invalid URI

Question 2

console API

Answer 2

contains several methods to aid in debugging

console. log()
console. error()
console. info()

Question 3

debugger statement

Answer 3

can be used in code to set a breakpoint

Question 4

additional console methods

Answer 4

console. warn() - writes a warning
console. table() - writes an object as a table
console. group() - creates a new inline group, which indents the output by an additional level
console. groupEnd() - exits the current inline group
console. assert() - writes an error messages if the specified expression is false
console. trace() - writes a stack trace to the console
console. time() - starts a timer
console. timeLog() - logs the value of the specified timer
console. timeEnd() - method ends a timer

Question 5

types of breakpoints

Answer 5

line-of-code: allows pausing code execution before a specific line of code; it can also be conditional

DOM change: pauses code execution on the code that changes a DOM node or its children

XHR / Fetch: pauses code execution when the request URL of an EXR contains a certain string

Event Listener: pauses on the event listener that runs after a specific event is executed

exception: pauses on the line of code that throws a caught or uncaught exception
function: pause code execution when a specific function is called

Question 6

setTimeout()

Answer 6

non blocking

Question 7

3 valid states of promises

Answer 7

pending, fulfilled, rejected

Question 8

promise methods

Answer 8

Promise.all - accepts an array or promises and returns a new promise; it is resolved when all the specified promises are resolved

Promise.allSettled - static method accepts an array of promises and returns the status and value/error for each promise

Promise.race - returns the first settled promise

Promise.any - when one of the promises is fulfilled, a single promise is returned

Promise.resolve - returns a new promise that resolves with the specified object

Promise.reject - returns a new promise that is rejected with the specified error

Question 9

stack

Answer 9

call stack contains functions that are being processed in which each function is stacked as a frame. after being processed, the function is popped out the call stack

Question 10

heap

Answer 10

objects that are created during runtime are allocated in a heap, which is a term used to describe a large region of memory in the running machine

Question 11

queue

Answer 11

message queue or callback/event queue

where an async callback waits to be pushed by the event loop into the call stack for processing

Question 12

specifying the events to monitor

Answer 12

monitorEvents
three ways of specifying the event or events to monitor for a given object
-event name
-array of events
-event type