2nd/10_Wiki/Topic_Programming/Topic_CSS/CSS_Variables_JavaScript.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
css-variables-and-javascript	CSS Variables and JavaScript	Frontend	draft	conceptual		CSS custom properties JavaScript setProperty CSS variable getPropertyValue change CSS variable with JS CSS variables DOM		B	0.88	2026-06-23	2026-06-23			css web frontend w3schools css-variables javascript dom	https://www.w3schools.com/css/css3_variables_javascript.asp

CSS Variables and JavaScript

🎯 한 줄 통찰 (One-line insight)

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]

🧠 핵심 개념 (Core concepts)

• DOM access — CSS variables have access to the DOM, which means you can change them with JavaScript. [S1]
• Reading a variable — get the computed styles for an element with getComputedStyle(), then read a specific variable with .getPropertyValue('--name'). [S1]
• Setting a variable — set a variable's value with element.style.setProperty('--name', 'value'). [S1]
• Root target — the example targets the :root element via document.querySelector(':root'), so the changed variable affects everything that references it. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Get pattern — getComputedStyle(el).getPropertyValue('--var') returns the current value of a CSS variable. [S1]
• Set pattern — el.style.setProperty('--var', newValue) reassigns a CSS variable at runtime, live-updating every rule that consumes it via var(). [S1]
• Single source, dynamic — by mutating one variable on :root, JavaScript can re-theme the page without touching individual rules. [S1]

📖 세부 내용 (Details)

Change Variables With JavaScript [S1] 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]

The example script: [S1]

<script>
// Get the root element
var r = document.querySelector(':root');

// Function for getting a variable value
function myFunction_get() {
  // Get the styles (properties and values) for the root
  var rs = getComputedStyle(r);
  // Alert the value of the --primary-bg-color variable
  alert("The value of --primary-bg-color is: " + rs.getPropertyValue('--primary-bg-color'));
}

// Function for setting a variable value
function myFunction_set() {
  // Set the value of variable --primary-bg-color to another value (in this case "green")
  r.style.setProperty('--primary-bg-color', 'green');
}
</script>

CSS var() function reference [S1]

Function	Description
var()	Inserts the value of a CSS variable

🛠️ 적용 사례 (Applied in summary)

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.

💻 코드 패턴 (Code patterns)

Read a CSS variable (language: JavaScript):

var r = document.querySelector(':root');
var rs = getComputedStyle(r);
var value = rs.getPropertyValue('--primary-bg-color');

Set a CSS variable (language: JavaScript):

var r = document.querySelector(':root');
r.style.setProperty('--primary-bg-color', 'green');

⚖️ 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: 0.88
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: CSS Tutorial
• 관련 개념: CSS Variables, CSS Variables in Media Queries, CSS @property, CSS var Function
• 참조 맥락: Referenced when a page needs to read or mutate CSS custom properties dynamically from JavaScript (e.g. theme switching).

📚 출처 (Sources)

• [S1] W3Schools — CSS Variables and JavaScript — https://www.w3schools.com/css/css3_variables_javascript.asp

📝 변경 이력 (Change history)

• 2026-06-23: Initial draft synthesized from the W3Schools "CSS Variables and JavaScript" page (Astra wiki-curation, P-Reinforce v3.1 format).