javascript-timers

Question 1

What is a “callback” function?

Answer 1

A callback function is:
a function passed into another function as an argument,
which is then invoked inside the outer function to
complete some kind of routine or action.

Question 2

Besides adding an event listener callback function to
an element or the document,

what is one way to delay the execution of
a JavaScript function until some point in the future?

setTimeout(functionRef, delay)

Answer 2

setTimeout(code)
setTimeout(code, delay)
setTimeout(functionRef)
setTimeout(functionRef, delay)
setTimeout(functionRef, delay, param1)
setTimeout(functionRef, delay, param1, param2)
setTimeout(functionRef, delay, param1, param2, /* … ,*/ paramN)

Parameters
- functionRef : A function to be executed after the timer expires.

• code : An alt syntax that
  allows you to include a string instead of a function,
  which is compiled and executed when the timer exp. (not recommended)
• delay (Optional) : The time, in milliseconds that the timer
  should wait BEFORE the specified function or code is executed.

       If this parameter is omitted, a value of 0 is used, 
       meaning execute "immediately", 
       or more accurately, the next event cycle.

Question 3

How can you set up a function to be called
repeatedly without using a loop?

Answer 3

To call a function repeatedly (e.g., every N milliseconds),
consider using setInterval().

The setInterval() method, offered on the Window and Worker interfaces, repeatedly calls a function or executes a code snippet,
with a fixed time delay between each call.

This method returns an interval ID
which uniquely identifies the interval,
so you can remove it later by calling clearInterval().

Question 4

What is the default time delay
if you omit the delay parameter from setTimeout() or setInterval()?

Answer 4

Both setTimeout and setInterval
Defaults to 0 if not specified.

Question 5

What do setTimeout() and setInterval() return?

Answer 5

The global setTimeout() method : sets a timer
which executes a function or specified piece of code
once the timer expires.

The returned timeoutID is a positive integer value
which identifies the timer created by the call to setTimeout().

This value can be passed to clearTimeout() to cancel the timeout.

Its GUARENTEED that a timeoutID value will never be reused by
a subsequent call to setTimeout() or setInterval() on the same object
(a window or a worker).

If setTimeout() is called with delay value that’s not a number,
implicit type coercion is silently done on
the value to convert it to a number.

Question 6

What does setInterval() return?

Answer 6

Return value: The returned intervalID is a numeric, non-zero value
which identifies the timer created by the call to setInterval();
this value can be passed to clearInterval() to cancel the interval.