It stores the date, time and provides methods for date/time management.… For instance, we can use it to store creation/modification times, to measure time, or just to print out… The first idea may be to run them many times in a row and measure the time difference.… Date and time in JavaScript are represented with the Date object.… Sometimes we need more precise time measurements.
The range: {3,5}, match 3-5 times
To find numbers from 3 to 5 digits we can put the limits into curly… That is, the character may repeat any times or be absent.… [a-z][a-z0-9]*>/i
We added an optional slash /? near the beginning of the pattern.… But as HTML has stricter restrictions for a tag name, <[a-z][a-z0-9]*> is more reliable.… Can we use <\w+> or we need <[a-z][a-z0-9]*>?
The time should be in CSS time format: in seconds s or milliseconds ms.
transition-delay.In transition-delay… But it becomes very simple if we devote a bit time to it.… We’ll make a timer: the digits will appear one by one, in a discrete way.… The transform will be split into 9 parts (10% each).… The time interval is automatically divided into 9 parts as well, so transition: 9s gives us 9 seconds
spread syntax in the chapter Rest parameters and spread syntax)
Using generators for iterables.Some time… Now we’d like to reuse it to generate a more complex sequence:
first, digits 0..9… It may take time. That’s not a problem: the generator will wait.… The third next(9) passes 9 into the generator as the result of the second yield and resumes the execution… Often we don’t use it, as most of time we want to get all returning values, but it can be useful when
Long time ago, when JavaScript language was created, Unicode encoding was simpler: there were no 4-byte… Hex_Digit includes hexadecimal digits: 0-9, a-f.
…And so on.… numbers.For instance, let’s look for hexadecimal numbers, written as xFF, where F is a hex digit (0…9
Canceling with clearTimeout.A call to setTimeout returns a “timer identifier” timerId that we can use… As we can see from alert output, in a browser the timer… For instance, Node.js returns a timer object with additional methods.… For browsers, timers are described in the timers section of HTML Living Standard.
setInterval.The setInterval… For example, the in-browser timer may slow down for a lot of reasons:
The CPU is overloaded.
Here [0-9A-F] has two ranges: it searches for a character that is either a digit from 0 to 9… classes are shorthands for certain character sets
For instance:
\d – is the same as [0-9]… For instance:
[^aeyo] – any character except 'a', 'e', 'y' or 'o'.
[^0-9] – any character except a
Although, on certain strings it takes a lot of time.… After some time it will suggest to reload the page.… For 123456789 we have n=9, that gives 511 combinations.… For n=30 – a thousand times more (1073741823 combinations).… The time needed to try a lot of (actually most of) combinations is now saved.
In binary form, 256 is 100000000 (9 bits), but Uint8Array only provides 8 bits per value, that makes… For 257, the binary form is 100000001 (9 bits), the rightmost 8 get stored, so we’ll have 1 in the array… We choose the format at method call time instead of the construction time.
HTML is like this:
The table has 9… We can add/remove <td> dynamically at any time and the highlighting will still work.… The HTML structure is flexible, we can add/remove buttons at any time.
These are numbers that we’re using most of the time, and we’ll talk about them in this chapter.… use cases for this are:
base=16 is used for hex colors, character encodings etc, digits can be 0..9… base=36 is the maximum, digits can be 0..9 or A..Z.
Most used are:
\d (“d” is from “digit”)
A digit: a character from 0 to 9.
Auto-repeat.If a key is being pressed for a long enough time, it starts to “auto-repeat”: the keydown… If it’s valid (from 0..9 or one of +-()), then it returns true, otherwise false.
timing(timeFraction)
Timing function, like CSS-property transition-timing-function that gets the fraction… The timing function is not limited by Bezier curves.… Timing functions.We saw the simplest, linear timing function above.
Let’s see more of them.… It falls down, then bounces back a few times and stops.… JavaScript animations can use any timing function.
Example: “time-formatted”.For example, there already exists <time> element in HTML, for date/time… Let’s create <time-formatted> element that displays the time in a nice, language-aware format:… Intl.DateTimeFormat data formatter, well-supported across the browsers, to show a nicely formatted time… At the end, we can easily make a live timer.… E.g, a search engine would be interested to know that we actually show a time.
It doesn’t matter if the task takes a long time.… If you run the code below, the engine will “hang” for some time.… There’s not much difference in the overall counting time.… If you run it, it’s easy to notice that it takes significantly less time.
Why?… And its overall execution time isn’t much longer.
Most of the time we can replace let by var or vice-versa and expect things to work:… But internally var is a very different beast, that originates from very old times… That’s because a long time ago in JavaScript, blocks had no Lexical Environments, and var is a remnant… With var, we can redeclare a variable any number of times… These differences make var worse than let most of the time.
Example: regexp for time.In previous articles there was a task to build a regexp for searching time in… It accepts 25:99 as the time (as 99 minutes match the pattern, but that time is invalid).
Most of the time, a JavaScript application needs to work with information.… known before execution (like a hexadecimal value for red) and some constants are calculated in run-time… In a real project, most of the time is spent modifying and extending an existing code base rather than… Please spend time thinking about the right name for a variable before declaring it.… Such programmers save a little bit on variable declaration but lose ten times more on debugging.
analogy for things we often have in programming:
A “producing code” that does something and takes time… The “producing code” takes whatever time it needs to produce the promised result, and the “promise” makes… We can add handlers any time: if the result is already there, they just execute.… We can call .then on a Promise as many times as we want.… Each time, we’re adding a new “fan”, a new subscribing function, to the “subscription list”.
prototypal inheritance was in the language since its dawn, but the ways to manage it evolved over time… The prototype property of a constructor function has worked since very ancient times.… implemented the non-standard __proto__ accessor that allowed the user to get/set a prototype at any time… on existing objects if speed matters
Technically, we can get/set [[Prototype]] at any time… But usually we only set it once at the object creation time and don’t modify it anymore: rabbit inherits
We’ll work with it most of the time.… numeric value:
elem.nodeType == 1 for element nodes,
elem.nodeType == 3 for text nodes,
elem.nodeType == 9
For a long time, JavaScript existed without a language-level module syntax.… The one-time evaluation has important consequences, that we should be aware of.… if executing a module code brings side-effects, like showing a message, then importing it multiple times… If we need to make something callable multiple times – we should export it as a function, like we did… If this module is imported from multiple files, the module is only evaluated the first time
They allow the code to be called many times without repetition.… Here we will see the message two times.… An argument is the value that is passed to the function when it is called (it’s a call time term).… On the other hand, it’s independently called every time when text is missing.… We are going to return to them many times, going more deeply into their advanced features.
Some time ago browsers used to show it as a message, but as the modern specification says, they shouldn… onload
[4] readyState:complete
[4] window onload
The numbers in square brackets denote the approximate time… Events labeled with the same digit happen approximately at the same time (± a few ms).… Here we can see that it happens in about the same time as img.onload (img is the last resource) and window.onload… loading – the document is loading.
interactive – the document is parsed, happens at about the same time
It also saves memory and time in case of reusing cached objects.… In order not to complicate our work, and not to notify third-party code every time our DOM-element is… In this case, the logger stops displaying messages and clears the timer.… FinalizationRegistry.Now it is time to talk about finalizers.… It is important to understand that during this time gap, the main program can make any changes to the
The value of this is evaluated during the run-time… In JavaScript this is “free”, its value is evaluated at call-time and does not depend on where the method… The concept of run-time evaluated this has both pluses and minuses.… The value of this is defined at run-time.
State 3 repeats every time a data packet is received over the network.… find readystatechange listeners in really old code, it’s there for historical reasons, as there was a time… Aborting request.We can terminate the request at any time.… If a synchronous call takes too much time, the browser may suggest to close the “hanging” webpage.… abort – upload aborted.
error – non-HTTP error.
load – upload finished successfully.
timeout – upload timed
In the greedy mode (by default) a quantified character is repeated as many times as possible.… It means: “repeat minimal number of times”.
We can enable it by putting a question mark '?'… Then the regular expression engine increases the number of repetitions for the dot and tries one more time… There are times when we need one or another.… Greedy
By default the regular expression engine tries to repeat the quantified character as many times
A code editor is the place where programmers spend most of their time.… above are those that either I or my friends whom I consider good developers have been using for a long time
The reason is simple: long, long time ago JavaScript was a much weaker language, many things could only… But that time passed a decade ago.
Right now, there’s almost no reason to use eval.
JavaScript also did not have any special methods to perform network requests at that time.… For a long time JavaScript was unable to do such requests.… Some time ago no one could even imagine that a webpage could make such requests.… The essential difference is that safe requests were doable since ancient times using <form> or… <script> tags, while unsafe were impossible for browsers for a long time.
there are many objects, and we try to walk and mark the whole object set at once, it may take some time… Idle-time collection – the garbage collector tries to run only while the CPU is idle, to reduce the possible… The V8 blog also publishes articles about changes in memory management from time to time.
It changes from time to time but should be similar.
Here we can see the red-colored error message.
Encoding strings.In old times, before URL objects appeared, people used strings for URLs.… replaced square brackets [...], that’s not correct, the reason is: IPv6 urls did not exist at the time… Such cases are rare, encode* functions work well most of the time.
Next time the request is sent to the same domain, the browser sends the cookie over the net using the… Limitations
There are a few limitations:
You can only set/update a single cookie at a time… automatically delete it (according to the browser’s time zone).… The browser sends cookies every time you visit the site bank.com, even if the form was submitted from… Such a protection takes time to implement though.
We can add, remove and read files from it at any time.… Here, the variable key may be calculated at run-time… So most of the time, when property names are known and simple, the dot is used.… Well, most of the time the comparison with undefined works fine.… JavaScript:
Array to store ordered data collections,
Date to store the information about the date and time
with the given text:
Most of the time… In practice, only insertAdjacentHTML is used most of the time.… These methods come from really ancient times.… The method comes from times when there was no DOM, no standards… Really old times.
other ways we’ve seen is that the function is created literally from a string, that is passed at run time… The code of that function is not known at the time of writing the script (that’s why we don’t use regular
But in the old times, there was no direct access to it.… F.prototype only used at new F time
F.prototype property is only used when new F is called
in-browser is a little special: it sets this=window for the function call (for Node.js, this becomes the timer… We can use it and not provide the first argument every time as it’s fixed with bind.
For instance, Date objects (to be covered in the chapter Date and time) can be subtracted, and the result… of date1 - date2 is the time difference between two dates.… Methods toString and valueOf come from ancient times.… That’s because in ancient times there was no good “error” concept in JavaScript.
The browser checks the mouse position from time to time.… According to the browser logic, the mouse cursor may be only over a single element at any time – the… The browser assumes that the mouse can be only over one element at one time – the deepest one.
That can lead to strange delays if transactions take a long time.
So, what to do?… Not every time. We can use event delegation instead.… a special object that traverses the object storage, given a query, and returns one key/value at a time… indexes do precisely the same as over object stores – they save memory by returning one value at a time… That works fine most of the time.
Let’s check whether or not a string is a time in 12:34 format.
A funny consequence
It is possible that at the same time… Should we remember these peculiarities all the time? Well, not really.… Actually, these tricky things will gradually become familiar over time, but there’s a solid way to avoid
Let’s note once again – it is possible to leave out semicolons most of the time.… Comments.As time goes on, programs become more and more complex.
comments the following situation is possible:
You (or your colleague) open the code written some time… You revert to the correct variant, but the time was wasted.
who comes across this line and tries to understand what is the value of i is going to have a merry time… And when there’s a typo… Ummm… We’re stuck for long, time to drink tea.… First, the code becomes longer and less readable, and the second, a fellow developer may spend a long time… reader may decide to look for a hidden meaning and meditate for an hour or two of their paid working time
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