Javascript error что это означает



Что значит JavaScript Error: учимся дебажить JavaScript на примерах

«JavaScript error, что это значит?» — именно такой вопрос задают многие пользователи операционной системы Windows, так как это одна из самых известных проблем с несовместимостью в этой ОС. Данная ошибка оповещает пользователя, что произошел какой-то сбой в определенном программном обеспечении. Многие проблемы подобного рода можно исправить самостоятельно, но некоторые из них могут исправить только квалифицированные специалисты.

JavaScript error, что это значит

JavaScript — это язык, на котором написано очень много фронтенда многих веб — ресурсов и приложений для компьютера. Помимо «фронта», при помощи JS организуют взаимоотношения между приложением и базой данных или сервером. Поэтому «JavaScript error» — это то, что может обозначать несколько популярных проблем:

  • нарушение в каких-либо процессах приложения ;
  • повреждение системных файлов;
  • отключение какой-либо службы;
  • и др.

Чаще всего таким ошибкам подвержены операционные системы Windows 7, 8 или 10, когда происходит запуск таких популярных программ , как Skype, Faceit, Discord или некоторых компьютерных игр. Подобные проблемы получаются из-за несовместимости программ и операционной системы. Какая именно из программ выдает подобную проблему — определить не сложно , так как именно при ее запуске система выдает оповещени е «JavaScript error».

Как исправить JavaScript error (ява скрипт эррор)?

  1. Первое , что необходимо выполнить , — это проверить компьютер на предмет заражения вирусом, потому что вирусы очень часто провоцируют подобные ошибки. А спонсором данного материала является сайт Уфавип, на котором размещены анкеты всех шлюх в Уфе из Черниковки. На нем вы непременно сможете подобрать проститутку, подходящую вам как в плане цены, так и в плане предоставляемых ею услуг. Если антивирус обнаружил вирус, то исключите его и попробуйте заново запустить приложение, которое вызвало проблему «JavaScript error».
  2. Нужно обновить программное обеспечение, которое вызвало ошибку , и саму операционную систему. Из-за отсутствия обновлений возникают подобные проблемы. А иногда ошибка может возникнуть из-за того , ч то один компонент обновился, а другой — нет : например, программу вы обновили, а ОС — нет. В результате выл езает «JavaScript error», а вы бежите в и нтернет узнавать, что это значит.
  3. Еще одним популярным решением является полный «снос» проблемного ПО, а потом его переустановка.
  4. Также при ошибке «JavaScript error» может помочь восстановление операционной системы до той даты, когда она функционировала нормально.

Иногда ошибки типа «JavaScript error» возникают не с компьютерными приложениями, а с веб — ресурсами, очень часто они возникают в соцсетях и мешают просматривать видео, фото и другой контент. Не нужно паниковать, так как подобные проблемы в основном решаются простым действием — нужно очистить кэш браузера. Сделать это можно через внутренние настройки браузера или с помощью дополнительных программ.

Заключение

JavaScript error имеет множество разновидностей, но практически все они решаются перечисленными выше действиями. Если ни один из способов вам не помог — это значит, что самое время обратиться в специализированный сервис, потому как есть шанс, что проблема расположена намного «глубже», чем может достать обычный пользователь.

Мы будем очень благодарны

если под понравившемся материалом Вы нажмёте одну из кнопок социальных сетей и поделитесь с друзьями.

Источник

What went wrong? Troubleshooting JavaScript

When you built up the «Guess the number» game in the previous article, you may have found that it didn’t work. Never fear — this article aims to save you from tearing your hair out over such problems by providing you with some tips on how to find and fix errors in JavaScript programs.

Prerequisites: Basic computer literacy, a basic understanding of HTML and CSS, an understanding of what JavaScript is.
Objective: To gain the ability and confidence to start fixing problems in your own code.

Types of error

Generally speaking, when you do something wrong in code, there are two main types of error that you’ll come across:

  • Syntax errors: These are spelling errors in your code that actually cause the program not to run at all, or stop working part way through — you will usually be provided with some error messages too. These are usually okay to fix, as long as you are familiar with the right tools and know what the error messages mean!
  • Logic errors: These are errors where the syntax is actually correct but the code is not what you intended it to be, meaning that program runs successfully but gives incorrect results. These are often harder to fix than syntax errors, as there usually isn’t an error message to direct you to the source of the error.
Читайте также:  Error 404 sans battle

Okay, so it’s not quite that simple — there are some other differentiators as you drill down deeper. But the above classifications will do at this early stage in your career. We’ll look at both of these types going forward.

An erroneous example

To get started, let’s return to our number guessing game — except this time we’ll be exploring a version that has some deliberate errors introduced. Go to GitHub and make yourself a local copy of number-game-errors.html (see it running live here).

  1. To get started, open the local copy inside your favorite text editor, and your browser.
  2. Try playing the game — you’ll notice that when you press the «Submit guess» button, it doesn’t work!

Note: You might well have your own version of the game example that doesn’t work, which you might want to fix! We’d still like you to work through the article with our version, so that you can learn the techniques we are teaching here. Then you can go back and try to fix your example.

At this point, let’s consult the developer console to see if it reports any syntax errors, then try to fix them. You’ll learn how below.

Fixing syntax errors

Earlier on in the course we got you to type some simple JavaScript commands into the developer tools JavaScript console (if you can’t remember how to open this in your browser, follow the previous link to find out how). What’s even more useful is that the console gives you error messages whenever a syntax error exists inside the JavaScript being fed into the browser’s JavaScript engine. Now let’s go hunting.

  1. Go to the tab that you’ve got number-game-errors.html open in, and open your JavaScript console. You should see an error message along the following lines:
  2. This is a pretty easy error to track down, and the browser gives you several useful bits of information to help you out (the screenshot above is from Firefox, but other browsers provide similar information). From left to right, we’ve got:
    • A red «x» to indicate that this is an error.
    • An error message to indicate what’s gone wrong: «TypeError: guessSubmit.addeventListener is not a function»
    • A «Learn More» link that links through to an MDN page that explains what this error means in greater detail.
    • The name of the JavaScript file, which links through to the Debugger tab of the developer tools. If you follow this link, you’ll see the exact line where the error is highlighted.
    • The line number where the error is, and the character number in that line where the error is first seen. In this case, we’ve got line 86, character number 3.
  3. If we look at line 86 in our code editor, we’ll find this line:

Warning: Error message may not be on line 86.

If you are using any code editor with an extension that launches a live server on your local machine, this will cause extra code to be injected. Because of this, the developer tools will list the error as occurring on a line that is not 86.

Note: See our TypeError: «x» is not a function reference page for more details about this error.

Syntax errors round two

  1. Save your page and refresh, and you should see the error has gone.
  2. Now if you try to enter a guess and press the Submit guess button, you’ll see another error!
  3. This time the error being reported is «TypeError: lowOrHi is null», on line 78.

Note: Null is a special value that means «nothing», or «no value». So lowOrHi has been declared and initialized, but not with any meaningful value — it has no type or value.

Note: This error didn’t come up as soon as the page was loaded because this error occurred inside a function (inside the checkGuess() < >block). As you’ll learn in more detail in our later functions article, code inside functions runs in a separate scope than code outside functions. In this case, the code was not run and the error was not thrown until the checkGuess() function was run by line 86.

Note: console.log() is a really useful debugging function that prints a value to the console. So it will print the value of lowOrHi to the console as soon as we have tried to set it in line 49.

element we want. Phew! Another error fixed! You can delete your console.log() line now, or keep it to reference later on — your choice.

Note: See our TypeError: «x» is (not) «y» reference page for more details about this error.

Syntax errors round three

  1. Now if you try playing the game through again, you should get more success — the game should play through absolutely fine, until you end the game, either by guessing the right number, or by running out of guesses.
  2. At that point, the game fails again, and the same error is spat out that we got at the beginning — «TypeError: resetButton.addeventListener is not a function»! However, this time it’s listed as coming from line 94.
  3. Looking at line number 94, it is easy to see that we’ve made the same mistake here. We again just need to change addeventListener to addEventListener . Do this now.

A logic error

At this point, the game should play through fine, however after playing through a few times you’ll undoubtedly notice that the «random» number you’ve got to guess is always 1. Definitely not quite how we want the game to play out!

There’s definitely a problem in the game logic somewhere — the game is not returning an error; it just isn’t playing right.

    Search for the randomNumber variable, and the lines where the random number is first set. The instance that stores the random number that we want to guess at the start of the game should be around line number 45:

Working through the logic

To fix this, let’s consider how this line is working. First, we invoke Math.random() , which generates a random decimal number between 0 and 1, e.g. 0.5675493843.

Next, we pass the result of invoking Math.random() through Math.floor() , which rounds the number passed to it down to the nearest whole number. We then add 1 to that result:

Rounding a random decimal number between 0 and 1 down will always return 0, so adding 1 to it will always return 1. We need to multiply the random number by 100 before we round it down. The following would give us a random number between 0 and 99:

Hence us wanting to add 1, to give us a random number between 1 and 100:

Try updating both lines like this, then save and refresh — the game should now play like we are intending it to!

Other common errors

There are other common errors you’ll come across in your code. This section highlights most of them.

SyntaxError: missing ; before statement

This error generally means that you have missed a semicolon at the end of one of your lines of code, but it can sometimes be more cryptic. For example, if we change this line inside the checkGuess() function:

It throws this error because it thinks you are trying to do something different. You should make sure that you don’t mix up the assignment operator ( = ) — which sets a variable to be equal to a value — with the strict equality operator ( === ), which tests whether one value is equal to another, and returns a true / false result.

Note: See our SyntaxError: missing ; before statement reference page for more details about this error.

The program always says you’ve won, regardless of the guess you enter

This could be another symptom of mixing up the assignment and strict equality operators. For example, if we were to change this line inside checkGuess() :

the test would always return true , causing the program to report that the game has been won. Be careful!

SyntaxError: missing ) after argument list

This one is pretty simple — it generally means that you’ve missed the closing parenthesis at the end of a function/method call.

Note: See our SyntaxError: missing ) after argument list reference page for more details about this error.

SyntaxError: missing : after property id

This error usually relates to an incorrectly formed JavaScript object, but in this case we managed to get it by changing

This has caused the browser to think that we are trying to pass the contents of the function into the function as an argument. Be careful with those parentheses!

SyntaxError: missing > after function body

This is easy — it generally means that you’ve missed one of your curly braces from a function or conditional structure. We got this error by deleting one of the closing curly braces near the bottom of the checkGuess() function.

SyntaxError: expected expression, got ‘string‘ or SyntaxError: unterminated string literal

These errors generally mean that you’ve left off a string value’s opening or closing quote mark. In the first error above, string would be replaced with the unexpected character(s) that the browser found instead of a quote mark at the start of a string. The second error means that the string has not been ended with a quote mark.

For all of these errors, think about how we tackled the examples we looked at in the walkthrough. When an error arises, look at the line number you are given, go to that line and see if you can spot what’s wrong. Bear in mind that the error is not necessarily going to be on that line, and also that the error might not be caused by the exact same problem we cited above!

Note: See our SyntaxError: Unexpected token and SyntaxError: unterminated string literal reference pages for more details about these errors.

Summary

So there we have it, the basics of figuring out errors in simple JavaScript programs. It won’t always be that simple to work out what’s wrong in your code, but at least this will save you a few hours of sleep and allow you to progress a bit faster when things don’t turn out right, especially in the earlier stages of your learning journey.

Источник

Оцените статью
toolgir.ru
Adblock
detector