2nd/10_Wiki/Topic_JavaScript/JavaScript_Function_Parameters.md

---
id: javascript-function-parameters
title: "JavaScript Function Parameters"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["function parameters", "arguments", "parameters vs arguments", "default parameters", "parameter rules", "function input"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.87
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["javascript", "js", "web", "frontend", "w3schools", "functions", "parameters"]
raw_sources: ["https://www.w3schools.com/js/js_function_parameters.asp"]
applied_in: []
github_commit: ""
---

# [[JavaScript Function Parameters]]

## 🎯 한 줄 통찰 (One-line insight)
Parameters are the named inputs a function declares in its parentheses; arguments are the real values passed in when it is called — and JavaScript checks neither their types nor their count. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Parameters pass values in** — parameters allow you to send values to a function and are listed inside the parentheses in the function definition. [S1]
- **Parameters vs arguments** — parameters are the names listed in the function definition; arguments are the real values passed to and received by the function. [S1]
- **No type or count enforcement** — JavaScript function definitions do not specify data types for parameters, do not perform type checking on arguments, and do not check the number of arguments received. [S1]
- **Missing arguments give wrong results** — accessing a function with an incorrect (missing) parameter can return an incorrect answer. [S1]
- **Default parameter values** — ECMAScript 2015 allows function parameters to have default values, used when no argument is provided. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **One or many parameters** — declare a single parameter, or as many as needed separated by commas. [S1]
- **Default fallback** — `function f(x, y = 10)` supplies `10` when the second argument is omitted. [S1]
- **No safety net** — because there is no type/count checking, a missing argument silently flows through (e.g. `toCelsius()` with no input). [S1]

## 📖 세부 내용 (Details)
**Parameters (Function Input)** — parameters allow you to pass (send) values to a function; they are listed inside the parentheses in the function definition. [S1]

**Functions with One Parameter** — a function can have one parameter: [S1]
```javascript
function sayHello(name) {
  return "Hello " + name;
}

let greeting = sayHello("John");
```

A single-parameter conversion: [S1]
```javascript
function toCelsius(fahrenheit) {
  return (5 / 9) * (fahrenheit - 32);
}

let value = toCelsius(77);
```

**Functions with Multiple Parameters** — you can add as many parameters as you want, separated by commas: [S1]
```javascript
function multiply(a, b) {
  return a * b;
}

let result = multiply(4, 5);
```
```javascript
function fullName(firstName, lastName) {
  return firstName + " " + lastName;
}

let name = fullName("John", "Doe");
```

**Parameters vs. Arguments** — parameters are the names listed in the function definition; arguments are the real values passed to and received by the function. [S1]

**Parameter Rules** — JavaScript function definitions do not specify data types for parameters; JavaScript functions do not perform type checking on the arguments; JavaScript functions do not check the number of arguments received. [S1]

**Incorrect Parameters** — accessing a function with an incorrect (missing) parameter can return an incorrect answer: [S1]
```javascript
function toCelsius(fahrenheit) {
  return (5/9) * (fahrenheit-32);
}

let value = toCelsius();
```

**Default Parameter Values** — ECMAScript 2015 allows function parameters to have default values; the default value is used if no argument is provided: [S1]
```javascript
function myFunction(x, y = 10) {
  return x + y;
}
myFunction(5);
```

## 🛠️ 적용 사례 (Applied in summary)
The page's own snippets are the canonical applied examples — single-parameter `sayHello(name)` and `toCelsius(fahrenheit)`, multi-parameter `multiply(a, b)` and `fullName(firstName, lastName)`, the missing-argument `toCelsius()` case, and the default-parameter `myFunction(x, y = 10)`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Multiple parameters (language: JavaScript):
```javascript
function fullName(firstName, lastName) {
  return firstName + " " + lastName;
}

let name = fullName("John", "Doe");
```
Default parameter value:
```javascript
function myFunction(x, y = 10) {
  return x + y;
}
myFunction(5);
```

## ⚖️ 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:** 0.87
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[JavaScript Tutorial]]
- **관련 개념:** [[JavaScript Functions]], [[JavaScript Function Definitions]], [[JavaScript Function Invocation]], [[JavaScript Function Returns]]
- **참조 맥락:** Referenced when designing a function's inputs, defaults, and how callers supply arguments.

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

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