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JavaScript - Coggle Diagram

- - - - Variables
        
        var
        
        let - that we can declare a variable without assigning the variable a value - like let aloe; Ключевое слово let подразумивает вохможность изменения переменной.
        
        const
        
        CONDITIONAL STATEMENTS
        
        If(true)
        
        if...else
        
        else if
        
        switch
        
        if...else statements allow us to automate solutions to yes-or-no questions, also known as binary decisions.
        Comparison Operators
        
        (>)
        
        <
        
        <=
        
        (>=)
        
        ===
        
        !==
        
        Logical operator
        
        (&&)
        2.(||)
        3.(!)
        
        Truthy and Falsy (Types)
        So which values are falsy— or evaluate to false when checked as a condition?
        The list of falsy values includes:
        0
        Empty strings like "" or ''
        null which represent when there is no value at all
        undefined which represent when a declared variable lacks a value
        NaN, or Not a Number
        
        Truthy and Falsy Assignment
        let defaultName = username || 'Stranger';
        Because || or statements check the left-hand condition first, the variable defaultName will be assigned the actual value of username if is truthy, and it will be assigned the value of 'Stranger' if username is falsy. This concept is also referred to as short-circuit evaluation.
        
        Ternary Operator
        isNightTime ? console.log('Turn on the lights!') : console.log('Turn off the lights!');
        
        SWITCH
        switch (groceryItem)
        case 'tomato':
        console.log('Tomatoes are $0.49');
        break;
        
        Functions
        
        Function Declarations
        function greetWorld(){
        console.log('Hello, World!');
        return true;
        }
        
        Hoisting - это возможность определять функции где угодно и она загрузится из памяти, и где бы ее не вызвали она сработает.
        Calling a Function
        getGreeting();
        Parameters and Arguments
        getGreeting(name, date);
        Default Parameters
        function greeting (name = 'stranger')
        
        Helper Functions
        We can use functions to section off small bits of logic or tasks, then use them when we need to. Writing helper functions can help take large and difficult tasks and break them into smaller and more manageable tasks.
        
        Function Expressions
        In a function expression, the function name is usually omitted. A function with no name is called an anonymous function. A function expression is often stored in a variable in order to refer to it.
        
        const calculateArea = function (width, height) {
        const area = width height;
        return area;
        };*
        
        Arrow Functions
        const fucntionName = () => {};
        const functionName = paramOne => {};
        const functionName = (paramOne, paramTwo) => {};
        Single-Line Block (Concise Body)
        const sumNumbers = number => number + number;
        Multi-Line Block
        const sumNumbers = number => {
        const sum = number + number;
        return sum;
        };
        **We can't use keyword "this"
        
        SCOPE
        Block scope and Global Scope
        Review - https://www.codecademy.com/courses/introduction-to-javascript/lessons/scope/exercises/review-scope
        
        Scope Pollution
        Scope pollution is when we have too many global variables that exist in the global namespace, or when we reuse variables across different scopes.
        
        Array
        let newYearsResolutions = ['Keep a journal', 'Take a falconry class', 'Learn to juggle'];
        Accessing Elements
        newYearsResolutions[0]
        Update Elements
        seasons[3] = 'Autumn';
        elements in an array declared with const remain mutable.
        .length - метод длины
        
        Methods/Properties
        
        length - длина
        
        push() - добавляем элемент в конец.
        
        .pop(), removes the last item of an array. Returns the value of the last element
        
        join() - объединяет все элементы массива в строку
        
        5.slice() - возвращает новый массив, содержащий копию части исходного
        6.splice() - изменяет содержимое массива, удаляя существующие элементы и/или добавляя новые.
        7.shift() - remove the first item from the array
        8.unshift() - добавляет один или более элементов в начало массива и возвращает новую длину массива.
        9.concat() - изменяет содержимое массива, удаляя существующие элементы и/или добавляя новые.
        
        Nested Arrays
        const nestedArr = [[1], [2, 3]];
        
        Loops
        
        5 more items...
      - String Interpolation
        ${myPet}
        a template literal is wrapped by backticks `
      - typeof operator
        If you need to check the data type of a variable’s value, you can use the typeof operator.
        The typeof operator checks the value to its right and returns, or passes back, a string of the data type.
- - - - forEach()
        iterator - () - callback function. Iterat all elements in array
        .map()
        .map() works in a similar manner to .forEach()— the major difference is that .map() returns a new array.
        .filter()
        However, .filter() returns an array of elements after filtering out certain elements from the original array. The callback function for the .filter() method should return true or false depending on the element that is passed to it.
        .findIndex()
        We sometimes want to find the location of an element in an array. That’s where the .findIndex() method comes in! Calling .findIndex() on an array will return the index of the first element that evaluates to true in the callback function.
        Calling .findIndex() on an array will return the index of the first element that evaluates to true in the callback function.
        If there isn’t a single element in the array that satisfies the condition in the callback, then .findIndex() will return -1.
        .reduce()
        method returns a single value after iterating through the elements of an array, thereby reducing the array.
      - Iteration Documentation
        https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#Iteration_methods
        
        The .some()
        method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.
        The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.
      - Objects
        We use curly braces, {}, to designate an object literal:
        let spaceship = {};
        Properties
        If we try to access a property that does not exist on that object, undefined will be returned.
        Bracket Notation
        spaceship['Active Duty']
        
        Property Assignment
        It’s important to know that although we can’t reassign an object declared with const, we can still mutate it, meaning we can add new properties and change the properties that are there.
        You can delete a property from an object with the delete operator.
        delete spaceship.mission;
        
        Method
        const alienShip =
        invade: function (){
        }
        }
        With the new method syntax introduced in ES6 we can omit the colon and the function keyword.
        const alienShip
        invade (){
        console.log('Hello! We have come to dominate your planet. Instead of Earth, it shall be called New Xaculon.')
        }
        
        Nested Objects
        Pass By Reference
        Objects are passed by reference. This means when we pass a variable assigned to an object into a function as an argument, the computer interprets the parameter name as pointing to the space in memory holding that object. As a result, functions which change object properties actually mutate the object permanently (even when the object is assigned to a const variable)
        Looping Through Objects - for...in
        Often use for log properties in object
        for (variable in object)
        statement
        
        Advanced Objects Introduction
        
        This keyword
        The this keyword references the calling object which provides access to the calling object’s properties.
        
        Arrow Functions and this - not return properties
        Arrow functions inherently bind, or tie, an already defined this value to the function itself that is NOT the calling object. In the code snippet above, the value of this is the global object, or an object that exists in the global scope, which doesn’t have a dietType property and therefore returns undefined.
        
        Privacy
        privacy fields or methods use annotation _fieldName
        Getters
        get fullName(){
        if (this._firstName && this._lastName){
        return ${this._firstName} ${this._lastName}
        }
        else{
        return 'Missing a first name or a last name.';
        }
        }
        
        person.fullname
        Setters
        
        Factory Function
        So far we’ve been creating objects individually, but there are times where we want to create many instances of an object quickly. Here’s where factory functions come in.
        A factory function is a function that returns an object and can be reused to make multiple object instances. Factory functions can also have parameters allowing us to customize the object that gets returned.
        Example
        const robotFactory = (model, mobile) => {
        }
        return {
        model: model,
        mobile: mobile,
        beep(){
        console.log('beep');
        }
        }
        
        Property Value Shorthand
        ES6 introduced some new shortcuts for assigning properties to variables known as destructuring.
        const monsterFactory = (name, age) => {
        return {
        name,
        age,
        }}
        
        Destructured Assignment
        https://www.codecademy.com/courses/introduction-to-javascript/lessons/advanced-objects/exercises/destruct-assign
        const {functionality} = robot
        This shortcut get method from object robot like a variable
        It works for Built-in Object Methods
        Object.keys()
        Object.entires()
        Object.assign()
  - - - Instance of class
        let Halley = new Dog(name, behavior)
        
        Methods
        class Dog {
        constructor(name){
        this._name = name
        }
        changeName(newName){
        return this._name = newName
        }
        }