Why you need to use try and catch in the JavaScript? | standard ES5

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Why you need to use try and catch in the JavaScript? | standard ES5

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Why you need to use try and catch in the JavaScript? | standard ES5

last updated: 1 Augusta 2020

Answer: for the code to run JavaScript to the end even if there is a run-time error.

Detailed explanation:
JavaScript code running and
if an error occurs at run time (refer to a function that does not exist, and so on) inside try{...}
we will immediately get into catch(error){...}
and the code will continue to run after the partition catch(error){...}

Example 1 using try catch

Html

<html>
<body>

<script>
          try
          {
               alert("Hello");
               // on the screen we will see "Hello"

               myBook(); // error!!!!!!!!

               alert("Bye");
          }
          catch (error)
          {
               alert(error);
               // on the screen we will see "ReferenceError: myBook is not defined"
          }

          alert("I am reading books!");
          // on the screen we will see "I am reading books!"
     </script>

</body>
</html>

Explanation of the example:

Execute alert("Hello");

Error myBook()

try is designed so that in case of an error we will immediately get into catch

Execute alert(error);

after completion catch

Execute alert("I am reading books!");

Example 2 DO NOT USE try catch

Html

<html>
<body>

<script>

     alert("Hello");
     // on the screen we will see "Hello"

     myBook(); // error !!!!!!

     alert("Bye");

</script>

</body>
</html>

Explanation of the example:

Execute alert("Hello");

Error myBook()

The program will end

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prototype - is a set of functions, variables for all instances of the class (as a function) in the JavaScript | standard ES5

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What are closures? (closure) in the JavaScript ? Standard ES5

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Объявления

Объявления

• In which editor (program) is it convenient to write JavaScript code?

New app

• Create a new application JavaScript in a text editor

• Create a new application JavaScript in Visual Studio Code. Debug the application. See in debugging how to perform JavaScript

Debugging JavaScript, HTML

• Debug JavaScript in Google Chrome. Using debugger

• How to find out (see) where the error is when executing HTML, JavaScript in Google Chrome

• Debugging JavaScript in the Google Chrome. Use console.log("Hello!")

JavaScript стандарт ES5. Издан в 2009 году. Поддерживается всеми браузерами

Function

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• Function return || in the JavaScript. Example: function getPersonName(name) { return name || "Evgen" } | standard ES5

• Call a function before it is defined (Hoisting) in the JavaScript | standard ES5

• Variables within a function (lifetime of variables within a function) JavaScript | standard ES5

• Pass parameters by value and by reference to the function in the JavaScript | standard ES5

• How to find out... whether there is a function by name in the JavaScript? Example: typeof calcSum == "function" | standard ES5

• The function described inside the function. JavaScript | standard ES5

Unnamed function

• Unnamed function in the JavaScript . Using an unnamed function: create a new variable and assign an unnamed function to a new variable. Example: var myFunc1 = function (a, b) { return a + b; } ; | standard ES5

• Unnamed function in the JavaScript . Using an unnamed function: pass an unnamed function as a parameter to another function. Example: Calculate(15, 7, function(v1, v2) {return v1+v2;}); | standard ES5

Само-вызывающая безымянная функция

• Self-calling unnamed function in the JavaScript. Where is it used? Used in Yandex advertising. Example: ( function(){ ... } )(); | standard ES5

• Create a file js with an object containing export variables and functions. This is an example of using a self-calling unnamed function | standard ES5

Lambda function (abbreviated version of the unnamed function)

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Variables

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• Accessing Variables Before Defining Them (Hoisting) in the JavaScript | standard ES5

• Variable scope var, let, const in the JavaScript | standard ES5

Text, strings in the JavaScript

• Text in the JavaScript. Class String. Example: var myText = String("World"); | standard ES5

• Length (string length in the JavaScript) | standard ES5

• Function replace(text1, text2) replace text in the JavaScript | standard ES5

• Function toUpperCase() converts text to uppercase JavaScript | standard ES5

• Function toLowerCase() lowercase text JavaScript | standard ES5

• Function split(delimiter) splits a string into substrings JavaScript | standard ES5

• Function charAt(position) get a symbol by position JavaScript | standard ES5

• Function substr(pos, len) returns a substring JavaScript | standard ES5

• Function slice(pos1, pos2) returns a substring JavaScript | standard ES5

• Function substring(pos1, pos2) returns a substring JavaScript | standard ES5

• Function indexOf(text, startPos) searches for a substring and returns an index JavaScript | standard ES5

• Function startsWith(text) Checks, whether the line begins with the specified substring JavaScript | standard ES5

• Function trim() remove spaces at the beginning and end of a line JavaScript | standard ES5

• Функция padStart(length, symbol) добавляет в начале строки символы до нужной длины строки JavaScript | стандарт ES5

• Функция padEnd(length, symbol) добавляет в конце строки символы до нужной длины строки JavaScript | стандарт ES5

• В текстовую переменную можно назначить текст как много строк. Пример: var myText = `Hello \n Thanks \n Bye` | JavaScript standard ES6

• In a text variable, you can write expressions with variables (formatting, string interpolation). Example: var myText = `Hello ${a}` | JavaScript standard ES6

Регулярные выражения

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Numbers and mathematical functions

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Date & Time

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Array

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• Найти min цены в сложном массиве: [ {name:"Tomate", price:10}, {name:"Apple", price:17}, {name:"Orange", price:15} ] в JavaScript | стандарт ES5

Collection Map and Set

• Collection "The key-meaning" in the JavaScript. Class Map | standard ES5

• Collection of unique values in the JavaScript. Class Set | standard ES5

Object {set of properties and functions}

• {} it's an object in the JavaScript. An object contains a set of properties and functions. Example var book = {Name: "Wizard of the Mediterranean", Price: 120}; | standard ES5

• {...} = объект в JavaScript заполняем из переменных класса или другим объектом. Пример: const {name, total, price} = b.myProps; | standard ES5

Class (it is a function using new) | стандарт ES5

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• prototype - is a set of functions, variables for all instances of the class (as a function) in the JavaScript | standard ES5

try catch

• Why you need to use try and catch in the JavaScript? | standard ES5

Closing (closure) in the Javascript

• What are closures? (closure) in the JavaScript ? Standard ES5

Управление памятью в JavaScript

• Управление памятью в JavaScript | standard ES5

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• Drawing a picture with movement and animation (sprite). Используем HTML элемент <canvas>. Для движения используем JavaScript: var img = new Image(), img.src = url, drawImage, timer, window.setInterval | standard ES5

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• PDF reader. Download and display a file PDF (JavaScript, HTML) | PDF JavaScript implemented by Mozilla

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• class | Class in the JavaScript. Example: class Book {...} ... var obj1 = new Book(); | стандарт ES6

• promise in the JavaScript | standard ES6

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