JavaScript Fundamentals and Core Concepts

JavaScript Language Overview

ECMAScript and JavaScript Relationship

ECMAScript serves as the specification standard for JavaScript, while JavaScript represents one implementation of this standard. The distinction arose when Netscape submitted JavaScript to ECMA International for standardization in 1996, leading to the ECMA-262 specification.

ECMAScript Version History

Year	Version	Key Features
1997	ES1	Initial release
1999	ES3	Regular expressions, try/catch
2009	ES5	Strict mode, JSON support
2015	ES6	Clases, modules
2016	ES7	Exponentiation operator, Array.includes

JavaScript Implementation Components

Core Language (ECMAScript)
Document Object Model (DOM)
Browser Object Model (BOM)

JavaScript Integration Methods

Inline Script

<script>
// JavaScript code here
</script>

External Script

<script src="script.js"></script>

Language Basics

Comments

// Single-line comment

/*
Multi-line
comment
*/

Variable Declaration

var userName = "John";
var userAge = 25;

ES6 Variable Declarations

let counter = 0;
const MAX_VALUE = 100;

Data Types

Dynamic Typing

var data;        // undefined
data = 42;       // number
data = "text";   // string

Number Type

var num1 = 3.14;
var num2 = 1000;
var num3 = 2e5;    // 200000

String Type

var greeting = "Hello";
var target = "World";
var message = greeting + " " + target;

String Methods

Method	Description
length	Returns string length
toUpperCase()	Converts to uppercase
indexOf()	Finds substring position
slice()	Extracts substring
split()	Splits into array

Template Strings (ES6)

const name = "Alice";
const greeting = `Hello ${name}, welcome!`;

Boolean Type

var isActive = true;
var isComplete = false;

Arrays

var items = ["apple", 123, true];
console.log(items[0]);  // "apple"

Array Methods

Method	Description
push()	Adds element to end
pop()	Removes last element
shift()	Removes first element
forEach()	Iterates through elements
map()	Creates new array

Type Checking

typeof "text"     // "string"
typeof 42        // "number"
typeof true      // "boolean"
typeof undefined // "undefined"

Operators

Arithmetic Operators

+ - * / % ++ --

Comparison Operators

== === != !== > < >= <=

Logical Operators

&& || !

Control Structures

Conditional Statements

if (score >= 90) {
    grade = 'A';
} else if (score >= 80) {
    grade = 'B';
} else {
    grade = 'C';
}

Switch Statement

switch(day) {
    case 0: dayName = "Sunday"; break;
    case 1: dayName = "Monday"; break;
    default: dayName = "Other";
}

Loops

for (let i = 0; i < 5; i++) {
    console.log(i);
}

let count = 0;
while (count < 5) {
    console.log(count);
    count++;
}

Ternary Operator

var result = condition ? value1 : value2;

Functions

Function Declaration

function calculateSum(a, b) {
    return a + b;
}

Function Expression

const multiply = function(a, b) {
    return a * b;
};

Arrow Functions (ES6)

const square = x => x * x;
const add = (x, y) => x + y;

Immediately Invoked Function

(function() {
    console.log("IIFE executed");
})();

Objects

Object Literal

const person = {
    firstName: "Jane",
    lastName: "Doe",
    age: 30
};

Object Property Access

console.log(person.firstName);
console.log(person["lastName"]);

Object Iteration

for (let key in person) {
    console.log(key + ": " + person[key]);
}

Built-in Objects

Date Object

const now = new Date();
console.log(now.toLocaleString());

JSON Handling

const jsonString = '{"name":"Bob","age":40}';
const obj = JSON.parse(jsonString);
const str = JSON.stringify(obj);

Regular Expressions

const pattern = /^[a-z]+$/i;
const isValid = pattern.test("Hello");

Math Object

Math.max(10, 20, 30);  // 30
Math.random();         // Random number 0-1
Math.floor(3.7);       // 3

Tags: ecmascript javascript ES6 DataTypes functions

Posted on Mon, 25 May 2026 20:46:26 +0000 by vince251

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