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

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

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Call a function before it is defined in the JavaScript | standard ES5

last updated: 1 Augusta 2020

Compiler in the JavaScript allows functions to be called before they are defined (in English it is called Hoisting).

Explanation

1st pass of the compiler

The compiler receives all function declarations. No code is executed and no functions are called.

Compiler Pass 2

Code execution occurs

Example 1

Html

<html>
<body>

<script>

     // call the function
     ShowMyText(); // we will see on the screen "Hello"

     // declare a function
     function ShowMyText()
     {
          alert("Hello");
     }

</script>

</body>
</html>

Example 2

Error if a function is declared as a variable and call the function before declaring a variable

Html

<html>
<body>

<script>

     // call the function
     ShowMyText(); // Error! ShowMyText = Undefined

     // declare a function
     var ShowMyText = function()
     {
          alert("Hello");
     }

</script>

</body>
</html>

Read: access to variables before they are defined in the JavaScript...

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

New app

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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

• Function in the JavaScript. Example: function CalculateSum(value1, value2) { ... } | standard ES5

• 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

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Lambda function (abbreviated version of the unnamed function)

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Variables

• Variables in the JavaScript (text, number, flag, date and time) | standard ES5

• 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

• Регулярные выражения в JavaScript | standard ES5

• Write a regular expression to remove all special characters except letters and numbers | Regex JavaScript | standard ES5

Numbers and mathematical functions

• Number in the JavaScript. Convert text to a number. Rounding a number. Convert hexadecimal to decimal. | standard ES5

• Mathematical functions from the library Math: Sin, cos, log, pow and so on in the JavaScript | standard ES5

Date & Time

• Date & Time (year, month, date, hours, minutes, seconds) in the JavaScript. Class Date | standard ES5

Array

• Array in the JavaScript This is [] or class Array | standard ES5

• Что значит 3 точки ...items | Пример 1: Math.max(...prices) | Пример 2: books.push(...items) | JavaScript, стандарт ES5

• Difference between push(items) and push(...items) | Adding an Array to an Array in the JavaScript | standard ES5

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

• 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

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• Class in the JavaScript this is a common constructor function. Such a constructor function contains simple data, objects, internal functions in the JavaScript. To create a class object, use new Example: function Book() { ... } ... var obj1 = new Book(); | стандарт ES5

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try catch

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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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• Анимация человечка в движении (sprite). Используем HTML элементы <div>, <img>. Для анимации используем CSS стили: "animation", "background-image", "background-position", "keyframes" | standard ES5

• Рисуем картинку с движением. Используем HTML элемент <canvas>. Для движения используем JavaScript: var img = new Image(), img.src = url, drawImage, timer, window.setInterval | standard ES5

• 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

Examples

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Do Popup using HTML and Javascript

• How to make a Popup window in a HTML page | Javascript, HTML, CSS

Моя игра (HTML, JavaScript)

• Моя игра "Wizard World" | HTML, JavaScript

PDF readers. Загрузка и отображение файла PDF (JavaScript, HTML)

• PDF reader. Загрузка и отображение файла PDF (adobe JavaScript, HTML) | PDF JavaScript implemented by Adobe

• 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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