---
id: javascript-introduction
title: "JavaScript Introduction"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["JavaScript", "JS", "JS intro", "ECMAScript", "client-side scripting"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.89
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools"]
raw_sources: ["https://www.w3schools.com/js/js_intro.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Introduction]]

## 🎯 한 줄 통찰 (One-line insight)
JavaScript is the programming language of the web — it programs the *behavior* of web pages, able to read and dynamically change both HTML content and CSS styles. [S1]

## 🧠 핵심 개념 (Core concepts)
- **JavaScript is the programming language of the web** — it lets you calculate, manipulate, and validate data, and update/change both HTML and CSS. [S1]
- **The three web layers** — HTML defines the content, CSS specifies the layout, and JavaScript programs the behavior. [S1]
- **The DOM entry point** — JavaScript reaches HTML elements through the document, most commonly with `document.getElementById()`, then reads/writes their content, attributes, and style. [S1]
- **Quotes are interchangeable** — JavaScript accepts both single `'` and double `"` quotes for strings. [S1]
- **Standardized** — JavaScript became an ECMA standard in 1997; the official standard is ECMA-262 and the official language name is ECMAScript. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Select → mutate pattern** — get a reference to an element (`document.getElementById("id")`), then assign to a property (`.innerHTML`, `.style.*`, an attribute) to change the page. [S1]
- **Style via `.style` object** — CSS properties are set in JS using camelCase property names on `element.style` (e.g. `fontSize`, not `font-size`). [S1]
- **Show/hide via display** — toggling `style.display` between `"none"` and `"block"` hides or reveals an element. [S1]

## 📖 세부 내용 (Details)
**What is JavaScript?**
JavaScript is the programming language of the web. It can calculate, manipulate, and validate data, and it can update and change both HTML and CSS. [S1]

**JavaScript, HTML and CSS**
The three layers of standard web technology: HTML to define the content of web pages, CSS to specify the layout of web pages, and JavaScript to program the behavior of web pages. [S1]

**JavaScript Can Change HTML Content**
One of many JavaScript HTML methods is `getElementById()`. It finds an HTML element (by id) and changes the element content (`innerHTML`): [S1]
```javascript
document.getElementById("demo").innerHTML = "Hello JavaScript";
```
JavaScript accepts both double and single quotes:
```javascript
document.getElementById('demo').innerHTML = 'Hello JavaScript';
```

**JavaScript Can Change HTML Attribute Values**
JavaScript can change attribute values dynamically — for example, changing the `src` (source) attribute of an `<img>` tag in response to user interaction (e.g. a light bulb turning on/off). [S1]

**JavaScript Can Change HTML Styles (CSS)**
Changing the style of an HTML element is a variant of changing an HTML attribute: [S1]
```javascript
document.getElementById("demo").style.fontSize = "35px";
```

**JavaScript Can Hide HTML Elements**
Hiding HTML elements can be done by changing the `display` style: [S1]
```javascript
document.getElementById("demo").style.display = "none";
```

**JavaScript Can Show HTML Elements**
Showing hidden HTML elements can also be done by changing the `display` style: [S1]
```javascript
document.getElementById("demo").style.display = "block";
```

**Why study JavaScript?**
JavaScript is one of the three languages all web developers must learn, alongside HTML and CSS. [S1]

**History**
JavaScript was invented by Brendan Eich in 1995 and became an ECMA standard in 1997. [S1]

## 🛠️ 적용 사례 (Applied in summary)
The page's own snippets are the canonical applied examples — selecting `#demo` and mutating its `innerHTML`, `style.fontSize`, and `style.display`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Select an element and change its content (language: JavaScript):
```javascript
document.getElementById("demo").innerHTML = "Hello JavaScript";
```
Change a style:
```javascript
document.getElementById("demo").style.fontSize = "35px";
```
Hide / show:
```javascript
document.getElementById("demo").style.display = "none";
document.getElementById("demo").style.display = "block";
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source.

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.89
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Where To]], [[JavaScript Output]], [[JavaScript HTML DOM]], [[HTML JavaScript]]
- **참조 맥락:** The entry point referenced whenever adding interactive behavior to an HTML/CSS page.

## 📚 출처 (Sources)
- [S1] W3Schools — JavaScript Introduction — https://www.w3schools.com/js/js_intro.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Introduction" page (Astra wiki-curation, P-Reinforce v3.1 format).