2nd/10_Wiki/Topics/Domain_Programming/Topic_JavaScript/JavaScript_Switch.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
javascript-switch	JavaScript Switch	Frontend	draft	conceptual		switch statement JS switch switch case case default break switch control flow		B	0.89	2026-06-23	2026-06-23			javascript js web frontend w3schools switch control-flow conditionals	https://www.w3schools.com/js/js_switch.asp

JavaScript Switch

🎯 한 줄 통찰 (One-line insight)

The switch statement selects one of many code blocks to execute by comparing an expression against case values using strict comparison (===). [S1]

🧠 핵심 개념 (Core concepts)

• Selects a code block by condition — based on a condition, switch selects one or more code blocks to be executed. [S1]
• break stops fall-through — when JavaScript reaches break, it breaks out of the switch block, preventing unmatched cases from also executing. [S1]
• default is the fallback — the default keyword specifies a block of code to run if there is no case match; it is optional. [S1]
• Strict comparison — switch uses strict comparison (===); values must match in both value and type. [S1]
• First match wins — if multiple cases match a case value, the first case is selected. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Evaluate once, branch many — the switch expression is evaluated once, then its value is compared against each case. [S1]
• Shared code blocks — multiple cases can share a single code block by listing cases back-to-back before the shared code. [S1]
• Default-not-last requires break — if default is not the last clause, terminate it with break so execution does not fall through. [S1]

📖 세부 내용 (Details)

Switch control flow [S1] Based on a condition, switch selects one or more code blocks to be executed.

Syntax [S1]

switch(expression) {
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
}

How it works [S1] The switch expression is evaluated once. The value of the expression is compared with the values of each case. If there is a match, the associated block of code is executed. If there is no match, no execution occurs (unless a default is present).

Example — weekday calculator [S1] The getDay() method returns the weekday as a number between 0 and 6 (Sunday=0, Monday=1, etc.).

switch (new Date().getDay()) {
  case 0:
    day = "Sunday";
    break;
  case 1:
    day = "Monday";
    break;
  case 2:
     day = "Tuesday";
    break;
  case 3:
    day = "Wednesday";
    break;
  case 4:
    day = "Thursday";
    break;
  case 5:
    day = "Friday";
    break;
  case 6:
    day = "Saturday";
}

The break keyword [S1] When JavaScript reaches a break keyword, it breaks out of the switch block. This stops the execution inside the switch block and prevents fall-through, where unmatched cases would otherwise also execute.

The default keyword [S1] The default keyword specifies the code to run if there is no case match.

switch (new Date().getDay()) {
  case 6:
    text = "Today is Saturday";
    break;
  case 0:
    text = "Today is Sunday";
    break;
  default:
    text = "Looking forward to the Weekend";
}

default not at the end [S1] When default is not the last clause, terminate it with break.

switch (new Date().getDay()) {
  default:
    text = "Looking forward to the Weekend";
    break;
  case 6:
    text = "Today is Saturday";
    break;
  case 0:
    text = "Today is Sunday";
}

Common code blocks [S1] Sometimes you will want different switch cases to use the same code; multiple cases can share a code block.

switch (new Date().getDay()) {
  case 4:
  case 5:
    text = "Soon it is Weekend";
    break;
  case 0:
  case 6:
    text = "It is Weekend";
    break;
  default:
    text = "Looking forward to the Weekend";
}

Switching details [S1] If multiple cases match a case value, the first case is selected. If no matching cases are found, the program continues to the default label. If no default label is found, the program continues to the statements after the switch.

Strict comparison [S1] Switch cases use strict comparison (===). The values must be of the same type to match. A strict comparison can only be true if the operands are of the same type. In this example there will be no match for x, because x is a string and the cases are numbers:

let x = "0";
switch (x) {
  case 0:
    text = "Off";
    break;
  case 1:
    text = "On";
    break;
  default:
    text = "No value found";
}

🛠️ 적용 사례 (Applied in summary)

The page's own snippets are the canonical applied examples — mapping new Date().getDay() to a weekday name, weekend detection via default, and grouping days with shared code blocks. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Basic switch with break and default:

switch(expression) {
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
}

Shared code block across cases:

switch (new Date().getDay()) {
  case 4:
  case 5:
    text = "Soon it is Weekend";
    break;
  case 0:
  case 6:
    text = "It is Weekend";
    break;
  default:
    text = "Looking forward to the Weekend";
}

⚖️ 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 If Else, JavaScript Ternary, JavaScript Break, JavaScript Comparisons
• 참조 맥락: Chosen over long if...else chains when branching on the discrete values of a single expression.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Switch — https://www.w3schools.com/js/js_switch.asp

📝 변경 이력 (Change history)

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