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W3Schools 튜토리얼을 P-Reinforce v3.1 포맷으로 위키화(영어 본문, 한/영 섹션 헤더). - Topic_HTML: 59문서 (튜토리얼+예제, 레퍼런스/메타 제외) - Topic_CSS: 190문서 (메인 + Advanced/Flexbox/Grid/RWD 전체) - Topic_JavaScript: 120문서 (코어 언어; Temporal/DOM상세/BOM/WebAPI/AJAX/jQuery/Graphics 등은 후속) 각 폴더 00_INDEX.md(MOC) 포함. 코드 verbatim, 미확인분은 "Not found in source" 표기. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
106 lines
4.9 KiB
Markdown
106 lines
4.9 KiB
Markdown
---
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id: css-variables-and-javascript
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title: "CSS Variables and JavaScript"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["CSS custom properties JavaScript", "setProperty CSS variable", "getPropertyValue", "change CSS variable with JS", "CSS variables DOM"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.88
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["css", "web", "frontend", "w3schools", "css-variables", "javascript", "dom"]
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raw_sources: ["https://www.w3schools.com/css/css3_variables_javascript.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[CSS Variables and JavaScript]]
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## 🎯 한 줄 통찰 (One-line insight)
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Because CSS variables (custom properties) have access to the DOM, JavaScript can read them with `getComputedStyle().getPropertyValue()` and overwrite them at runtime with `element.style.setProperty()`. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **DOM access** — CSS variables have access to the DOM, which means you can change them with JavaScript. [S1]
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- **Reading a variable** — get the computed styles for an element with `getComputedStyle()`, then read a specific variable with `.getPropertyValue('--name')`. [S1]
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- **Setting a variable** — set a variable's value with `element.style.setProperty('--name', 'value')`. [S1]
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- **Root target** — the example targets the `:root` element via `document.querySelector(':root')`, so the changed variable affects everything that references it. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Get pattern** — `getComputedStyle(el).getPropertyValue('--var')` returns the current value of a CSS variable. [S1]
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- **Set pattern** — `el.style.setProperty('--var', newValue)` reassigns a CSS variable at runtime, live-updating every rule that consumes it via `var()`. [S1]
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- **Single source, dynamic** — by mutating one variable on `:root`, JavaScript can re-theme the page without touching individual rules. [S1]
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## 📖 세부 내용 (Details)
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**Change Variables With JavaScript** [S1]
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CSS variables have access to the DOM, which means that you can change them with JavaScript. The page presents an example of a script that displays and changes the `--primary-bg-color` variable from the example used in the previous pages. (The page notes you do not need to be familiar with JavaScript yet, and links to the W3Schools JavaScript Tutorial.) [S1]
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The example script: [S1]
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```javascript
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<script>
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// Get the root element
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var r = document.querySelector(':root');
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// Function for getting a variable value
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function myFunction_get() {
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// Get the styles (properties and values) for the root
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var rs = getComputedStyle(r);
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// Alert the value of the --primary-bg-color variable
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alert("The value of --primary-bg-color is: " + rs.getPropertyValue('--primary-bg-color'));
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}
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// Function for setting a variable value
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function myFunction_set() {
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// Set the value of variable --primary-bg-color to another value (in this case "green")
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r.style.setProperty('--primary-bg-color', 'green');
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}
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</script>
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```
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**CSS `var()` function reference** [S1]
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| Function | Description |
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|----------|-------------|
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| `var()` | Inserts the value of a CSS variable |
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own applied example is a getter/setter script pair: `myFunction_get()` alerts the current `--primary-bg-color` value, and `myFunction_set()` reassigns it to `green` on the `:root` element. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Read a CSS variable (language: JavaScript):
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```javascript
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var r = document.querySelector(':root');
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var rs = getComputedStyle(r);
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var value = rs.getPropertyValue('--primary-bg-color');
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```
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Set a CSS variable (language: JavaScript):
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```javascript
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var r = document.querySelector(':root');
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r.style.setProperty('--primary-bg-color', 'green');
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```
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source.
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.88
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[CSS Tutorial]]
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- **관련 개념:** [[CSS Variables]], [[CSS Variables in Media Queries]], [[CSS @property]], [[CSS var Function]]
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- **참조 맥락:** Referenced when a page needs to read or mutate CSS custom properties dynamically from JavaScript (e.g. theme switching).
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## 📚 출처 (Sources)
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- [S1] W3Schools — CSS Variables and JavaScript — https://www.w3schools.com/css/css3_variables_javascript.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Variables and JavaScript" page (Astra wiki-curation, P-Reinforce v3.1 format).
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