2nd/10_Wiki/Topics/Domain_Programming/Topic_JavaScript/JavaScript_Loops.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-loops	JavaScript Loops	Frontend	draft	conceptual		loops JS loops for loop while loop do while iteration		B	0.88	2026-06-23	2026-06-23			javascript js web frontend w3schools loops iteration control-flow	https://www.w3schools.com/js/js_loops.asp

JavaScript Loops

🎯 한 줄 통찰 (One-line insight)

Loops let you run the same block of code many times, each time with a different value — replacing long repetitive sequences with a compact iteration. [S1]

🧠 핵심 개념 (Core concepts)

• Loops repeat a block of code — they execute a code block multiple times, often with a different value each pass. [S1]
• for loop — uses three expressions: an initializer, a condition, and an update run after each iteration. [S1]
• while loop — runs as long as a specified condition is true. [S1]
• do/while loop — a variant that runs the block at least once before checking the condition. [S1]
• Loop scope — variables declared with let inside a loop are visible only within the loop, unlike var. [S1]
• Infinite-loop hazard — forgetting to update the condition variable means the loop never ends and crashes the browser. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Replace repetition with iteration — instead of writing the same statement for each array index, loop over cars.length. [S1]
• Index accumulation — append each iteration's value into a result string (text += ...). [S1]
• Always advance the condition variable — increment (e.g. i++) so the condition eventually becomes false. [S1]

📖 세부 내용 (Details)

Why loops [S1] Loops are handy if you want to run the same code over and over again, each time with a different value. Instead of writing the same statement many times:

text += cars[0] + "<br>";
text += cars[1] + "<br>";
text += cars[2] + "<br>";
text += cars[3] + "<br>";
text += cars[4] + "<br>";
text += cars[5] + "<br>";

You can write:

for (let i = 0; i < cars.length; i++) {
  text += cars[i] + "<br>";
}

The for loop [S1] The for loop has the syntax for (expr1; expr2; expr3) { // code block to be executed }.

for (let i = 0; i < 5; i++) {
  text += "The number is " + i + "<br>";
}

Loop scope — var vs let [S1] Using var in a loop, the loop variable redeclares the outer variable:

let i = 5;

for (i = 0; i < 10; i++) {
  // some code
}

// Here i is 10

Using let in a loop, the loop variable is scoped only to the loop:

let i = 5;

for (let i = 0; i < 10; i++) {
  // some code
}

// Here i is 5

The while loop [S1] The while loop has the syntax while (condition) { // code block to be executed }.

while (i < 10) {
  text += "The number is " + i;
  i++;
}

Note: If you forget to increase the variable used in the condition, the loop will never end. This will crash your browser.

The do/while loop [S1] The do/while loop has the syntax do { // code block to be executed } while (condition);.

do {
  text += "The number is " + i;
  i++;
}
while (i < 10);

Note: The do while runs at least once, even if the condition is false from the start.

Different kinds of loops [S1] JavaScript supports the for loop (loops through a block of code a number of times), the for/in loop (loops through the properties of an object), the for/of loop (loops through the values of an iterable object), the while loop (loops through a block of code while a condition is true), and the do/while loop (also loops while a condition is true).

🛠️ 적용 사례 (Applied in summary)

The page's own snippets are the canonical applied examples — replacing repeated text += cars[n] statements with a for loop over cars.length, and accumulating numbers in for/while/do-while loops. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Iterate an array:

for (let i = 0; i < cars.length; i++) {
  text += cars[i] + "<br>";
}

While loop with advancing counter:

while (i < 10) {
  text += "The number is " + i;
  i++;
}

Do-while (runs at least once):

do {
  text += "The number is " + i;
  i++;
}
while (i < 10);

⚖️ 비교 및 선택 기준 (Comparison & decision criteria)

• for vs while — use for when the number of iterations / the counter is known up front (init, condition, update in one place); use while when looping purely on a condition. [S1]
• while vs do/while — use do/while when the block must run at least once even if the condition is initially false. [S1]
• let vs var for the loop variable — let keeps the counter scoped to the loop; var leaks it to the surrounding scope. [S1]

⚖️ 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: JavaScript Tutorial
• 관련 개념: JavaScript For Loop, JavaScript While Loop, JavaScript Break, JavaScript Booleans
• 참조 맥락: The overview entry point for all iteration constructs; specific loop types are detailed in their own pages.

📚 출처 (Sources)

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

📝 변경 이력 (Change history)

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