Flashcards
JavaScript
Flashcards do conjunto (33)
- 1JavaScriptJavaScript is a programming language that powers the dynamic behavior on most websites. Alongside HTML and CSS, it is a core technology that makes the web run.
- 2MethodsMethods return information about an object, and are called by appending an instance with a period ., the method name, and parentheses.
// Returns a number between 0 and 1
Math.random();
You can find a list of built-in string methods in the JavaScript documentation. Developers use documentation as a reference tool. It describes JavaScript’s keywords, methods, and syntax.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String
Methoden geben Informationen über ein Objekt zurück und werden aufgerufen, indem eine Instanz mit einem Punkt ., dem Methodennamen und Klammern angehängt wird. - 3LibrariesLibraries contain methods that can be called by appending the library name with a period ., the method name, and a set of parentheses.
Math.random();
// ☝️ Math is the library - 4console.log()The console.log() method is used to log or print messages to the console. It can also be used to print objects and other info.
console.log('Hi there!');
// Prints: Hi there! - 5NumbersNumbers are a primitive data type. They include the set of all integers and floating point numbers.
let amount = 6;
let price = 4.99; - 6String .lengthThe .length property of a string returns the number of characters that make up the string.
let message = 'good nite';
console.log(message.length);
// Prints: 9
console.log('howdy'.length);
// Prints: 5 - 7Data InstancesWhen a new piece of data is introduced into a JavaScript program, the program keeps track of it in an instance of that data type. An instance is an individual case of a data type.
- 8BooleansBooleans are a primitive data type. They can be either true or false.
let lateToWork = true; - 9Math.random()The Math.random() function returns a floating-point, random number in the range from 0 (inclusive) up to but not including 1.
console.log(Math.random());
// Prints: 0 - 0.9 - 10Math.floor()The Math.floor() function returns the largest integer less than or equal to the given number.
console.log(Math.floor(5.95));
// Prints: 5 - 11Single Line CommentsIn JavaScript, single-line comments are created with two consecutive forward slashes //.
// This line will denote a comment - 12NullNull is a primitive data type. It represents the intentional absence of value. In code, it is represented as null.
let x = null; - 13StringsStrings are a primitive data type. They are any grouping of characters (letters, spaces, numbers, or symbols) surrounded by single quotes ' or double quotes ".
let single = 'Wheres my bandit hat?';
let double = "Wheres my bandit hat?"; - 14Arithmetic OperatorsJavaScript supports arithmetic operators for:
+ addition
- subtraction
* multiplication
/ division
% modulo
// Addition
5 + 5
// Subtraction
10 - 5
// Multiplication
5 * 10
// Division
10 / 5
// Modulo
10 % 5 - 15Multi-line CommentsIn JavaScript, multi-line comments are created by surrounding the lines with /* at the beginning and */ at the end. Comments are good ways for a variety of reasons like explaining a code block or indicating some hints, etc.
/*
The below configuration must be
changed before deployment.
*/
let baseUrl = 'localhost/taxwebapp/country'; - 16Remainder / Modulo OperatorThe remainder operator, sometimes called modulo, returns the number that remains after the right-hand number divides into the left-hand number as many times as it evenly can.
// calculates # of weeks in a year, rounds down to nearest integer
const weeksInYear = Math.floor(365/7);
// calcuates the number of days left over after 365 is divded by 7
const daysLeftOver = 365 % 7 ;
console.log("A year has " + weeksInYear + " weeks and " + daysLeftOver + " days"); - 17Assignment OperatorsAn assignment operator assigns a value to its left operand based on the value of its right operand. Here are some of them:
+= addition assignment
-= subtraction assignment
*= multiplication assignment
/= division assignment
let number = 100;
// Both statements will add 10
number = number + 10;
number += 10;
console.log(number);
// Prints: 120 - 18String InterpolationString interpolation is the process of evaluating string literals containing one or more placeholders (expressions, variables, etc).
It can be performed using template literals: text ${expression} text.
let age = 7;
// String concatenation
'Tommy is ' + age + ' years old.';
// String interpolation
`Tommy is ${age} years old.`; - 19VariablesVariables are used whenever there’s a need to store a piece of data. A variable contains data that can be used in the program elsewhere. Using variables also ensures code re-usability since it can be used to replace the same value in multiple places.
const currency = '$';
let userIncome = 85000;
console.log(currency + userIncome + ' is more than the average income.');
// Prints: $85000 is more than the average income. - 20Undefinedundefined is a primitive JavaScript value that represents lack of defined value. Variables that are declared but not initialized to a value will have the value undefined.
var a;
console.log(a);
// Prints: undefined - 21Learn Javascript: VariablesA variable is a container for data that is stored in computer memory. It is referenced by a descriptive name that a programmer can call to assign a specific value and retrieve it.
// examples of variables
let name = "Tammy";
const found = false;
var age = 3;
console.log(name, found, age);
// Tammy, false, 3 - 22Declaring VariablesTo declare a variable in JavaScript, any of these three keywords can be used along with a variable name:
var is used in pre-ES6 versions of JavaScript.
let is the preferred way to declare a variable when it can be reassigned.
const is the preferred way to declare a variable with a constant value.
var age;
let weight;
const numberOfFingers = 20; - 23Template LiteralsTemplate literals are strings that allow embedded expressions, ${expression}. While regular strings use single ' or double " quotes, template literals use backticks instead.
let name = "Codecademy";
console.log(`Hello, ${name}`);
// Prints: Hello, Codecademy
console.log(`Billy is ${6+8} years old.`);
// Prints: Billy is 14 years old. - 24let Keywordlet creates a local variable in JavaScript & can be re-assigned. Initialization during the declaration of a let variable is optional. A let variable will contain undefined if nothing is assigned to it.
let count;
console.log(count); // Prints: undefined
count = 10;
console.log(count); // Prints: 10 - 25const KeywordA constant variable can be declared using the keyword const. It must have an assignment. Any attempt of re-assigning a const variable will result in JavaScript runtime error.
const numberOfColumns = 4;
numberOfColumns = 8;
// TypeError: Assignment to constant variable. - 26String ConcatenationIn JavaScript, multiple strings can be concatenated together using the + operator. In the example, multiple strings and variables containing string values have been concatenated. After execution of the code block, the displayText variable will contain the concatenated string.
let service = 'credit card';
let month = 'May 30th';
let displayText = 'Your ' + service + ' bill is due on ' + month + '.';
console.log(displayText);
// Prints: Your credit card bill is due on May 30th. - 27ConsoleThe console is a panel that displays important messages, like errors, for developers. Much of the work the computer does with our code is invisible to us by default. If we want to see things appear on our screen, we can print, or log, to our console directly.
- 28Data TypesNumber: Any number, including numbers with decimals: 4, 8, 1516, 23.42.
String: Any grouping of characters on your keyboard (letters, numbers, spaces, symbols, etc.) surrounded by single quotes: ' ... ' or double quotes " ... ". Though we prefer single quotes. Some people like to think of string as a fancy word for text.
Boolean: This data type only has two possible values— either true or false (without quotes). It’s helpful to think of booleans as on and off switches or as the answers to a “yes” or “no” question.
Null: This data type represents the intentional absence of a value, and is represented by the keyword null (without quotes).
Undefined: This data type is denoted by the keyword undefined (without quotes). It also represents the absence of a value though it has a different use than null.
Symbol: A newer feature to the language, symbols are unique identifiers, useful in more complex coding. No need to worry about these for now.
Object: Collections of related data. - 29String ConcatenationOperators aren’t just for numbers! When a + operator is used on two strings, it appends the right string to the left string:
console.log('hi' + 'ya'); // Prints 'hiya'
console.log('wo' + 'ah'); // Prints 'woah'
console.log('I love to ' + 'code.')
// Prints 'I love to code.'
This process of appending one string to another is called concatenation. Notice in the third example we had to make sure to include a space at the end of the first string. The computer will join the strings exactly, so we needed to make sure to include the space we wanted between the two strings. - 30PropertiesWhen you introduce a new piece of data into a JavaScript program, the browser saves it as an instance of the data type. Every string instance has a property called length that stores the number of characters in that string. You can retrieve property information by appending the string with a period and the property name:
console.log('Hello'.length); // Prints 5 - 31ObjectsIn addition to console, there are other objects built into JavaScript. Down the line, you’ll build your own objects, but for now these “built-in” objects are full of useful functionality.
The great thing about objects is that they have methods! Let’s call the .random() method from the built-in Math object:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects - 32FunctionsA function is a sequence of instructions that performs a specific task, packaged as a unit.
When we define a function, we specify the instructions, inputs, and name of the function.
When we call a function, all of its instructions are executed.
Functions can be executed many times, making its instructions reusable.
Functions can have parameters, which accept input values, making its instructions flexible.
Functions organize a program into distinct units, making interchanging and editing them easier. This makes your entire program organized and modular. - 33OperatorsOperators are symbols that represent different ways of modifying, comparing, and evaluating information.
Arithmetic operators are used to make calculations.
Comparison operators determine the relationship between two values, which results in a boolean.
Logical operators determine the logical state of multiple boolean values or expressions, which results in another boolean.
Informações
- Descrição
- Erklärung alle Synthax Befehle
- Criado por
- Niklas Jaschinski
- Visualizações
- 12
- Tags
- Avaliação