Javascript Syntax: Intro Flashcards
console.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.
JavaScript
JavaScript 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.
Methods
Methods return information about an object, and are called by appending an instance with a period ., the method name, and parentheses.
Libraries
Libraries contain methods that can be called by appending the library name with a period ., the method name, and a set of parentheses.
Numbers
Numbers are a primitive data type. They include the set of all integers and floating point numbers.
String .length
The .length property of a string returns the number of characters that make up the string.
Data Instances
When 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.
Booleans
Booleans are a primitive data type. They can be either true or false.
Math.random()
The Math.random() function returns a floating-point, random number in the range from 0 (inclusive) up to but not including 1.
Math.floor()
The Math.floor() function returns the largest integer less than or equal to the given number.
Single Line Comments
In JavaScript, single-line comments are created with two consecutive forward slashes //.
Null
Null is a primitive data type. It represents the intentional absence of value. In code, it is represented as null.
Strings
Strings are a primitive data type. They are any grouping of characters (letters, spaces, numbers, or symbols) surrounded by single quotes ‘ or double quotes “.
Arithmetic Operators
JavaScript supports arithmetic operators for:
\+ addition - subtraction * multiplication / division % modulo
Multi-line Comments
In 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.
Remainder / Modulo Operator
The 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.
Assignment Operators
An 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
String Interpolation
String 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.
Variables
Variables 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.
Undefined
undefined 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.
Learn Javascript: Variables
A 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.
Declaring Variables
To 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.
Template Literals
Template literals are strings that allow embedded expressions, ${expression}. While regular strings use single ‘ or double “ quotes, template literals use backticks instead.
let Keyword
let 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.
const Keyword
A 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.
String Concatenation
In 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.
