JavaScript の力を解き放つ: プロのヒントとテクニック

1. Use destructuring for swapping variables

let a = 1, b = 2;
[a, b] = [b, a];
console.log(a, b); // 2 1

Why: Provides a clean, one-line way to swap variable values without a temporary variable.

2. Use template literals for string interpolation

const name = "Alice";
console.log(`Hello, ${name}!`); // Hello, Alice!

Why: Makes string concatenation more readable and less error-prone than traditional methods.

3. Use the nullish coalescing operator (??) for default values

const value = null;
const defaultValue = value ?? "Default";
console.log(defaultValue); // "Default"

Why: Provides a concise way to handle null or undefined values, distinguishing from falsy values like 0 or empty string.

4. Use optional chaining (?.) for safe property access

const obj = { nested: { property: "value" } };
console.log(obj?.nested?.property); // "value"
console.log(obj?.nonexistent?.property); // undefined

Why: Prevents errors when accessing nested properties that might not exist, reducing the need for verbose checks.

5. Use the spread operator (...) for array manipulation

const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];
const combined = [...arr1, ...arr2];
console.log(combined); // [1, 2, 3, 4, 5, 6]

Why: Simplifies array operations like combining, copying, or adding elements, making code more concise and readable.

6. Use Array.from() to create arrays from array-like objects

const arrayLike = { 0: "a", 1: "b", 2: "c", length: 3 };
const newArray = Array.from(arrayLike);
console.log(newArray); // ["a", "b", "c"]

Why: Easily converts array-like objects or iterables into true arrays, enabling use of array methods.

7. Use Object.entries() for easy object iteration

const obj = { a: 1, b: 2, c: 3 };
for (const [key, value] of Object.entries(obj)) {
  console.log(`${key}: ${value}`);
}

Why: Provides a clean way to iterate over both keys and values of an object simultaneously.

8. Use Array.prototype.flat() to flatten nested arrays

const nestedArray = [1, [2, 3, [4, 5]]];
console.log(nestedArray.flat(2)); // [1, 2, 3, 4, 5]

Why: Simplifies working with nested arrays by flattening them to a specified depth.

9. Use async/await for cleaner asynchronous code

async function fetchData() {
  try {
    const response = await fetch('https://api.example.com/data');
    const data = await response.json();
    console.log(data);
  } catch (error) {
    console.error('Error:', error);
  }
}

Why: Makes asynchronous code look and behave more like synchronous code, improving readability and error handling.

10. Use Set for unique values in an array

const numbers = [1, 2, 2, 3, 4, 4, 5];
const uniqueNumbers = [...new Set(numbers)];
console.log(uniqueNumbers); // [1, 2, 3, 4, 5]

Why: Provides an efficient way to remove duplicates from an array without manual looping.

11. Use Object.freeze() to create immutable objects

const frozenObj = Object.freeze({ prop: 42 });
frozenObj.prop = 100; // Fails silently in non-strict mode
console.log(frozenObj.prop); // 42

Why: Prevents modifications to an object, useful for creating constants or ensuring data integrity.

12. Use Array.prototype.reduce() for powerful array transformations

const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((acc, curr) => acc + curr, 0);
console.log(sum); // 15

Why: Allows complex array operations to be performed in a single pass, often more efficiently than loops.

13. Use the logical AND operator (&&) for conditional execution

const isTrue = true;
isTrue && console.log("This will be logged");

Why: Provides a short way to execute code only if a condition is true, without an explicit if statement.

14. Use Object.assign() to merge objects

const obj1 = { a: 1, b: 2 };
const obj2 = { b: 3, c: 4 };
const merged = Object.assign({}, obj1, obj2);
console.log(merged); // { a: 1, b: 3, c: 4 }

Why: Simplifies object merging, useful for combining configuration objects or creating object copies with overrides.

15. Use Array.prototype.some() and Array.prototype.every() for array

checking
const numbers = [1, 2, 3, 4, 5];
console.log(numbers.some(n => n > 3)); // true
console.log(numbers.every(n => n > 0)); // true

Why: Provides concise ways to check if any or all elements in an array meet a condition, avoiding explicit loops.

16. Use console.table() for better logging of tabular data

const users = [
  { name: "John", age: 30 },
  { name: "Jane", age: 28 },
];
console.table(users);

Why: Improves readability of logged data in tabular format, especially useful for arrays of objects.

17. Use Array.prototype.find() to get the first matching element

const numbers = [1, 2, 3, 4, 5];
const found = numbers.find(n => n > 3);
console.log(found); // 4

Why: Efficiently finds the first element in an array that satisfies a condition, stopping iteration once found.

18. Use Object.keys(), Object.values(), and Object.entries() for object

manipulation
const obj = { a: 1, b: 2, c: 3 };
console.log(Object.keys(obj)); // ["a", "b", "c"]
console.log(Object.values(obj)); // [1, 2, 3]
console.log(Object.entries(obj)); // [["a", 1], ["b", 2], ["c", 3]]

Why: Provides easy ways to extract and work with object properties and values, useful for many object operations.

19. Use the Intl API for internationalization

const number = 123456.789;
console.log(new Intl.NumberFormat('de-DE').format(number)); // 123.456,789

Why: Simplifies formatting of numbers, dates, and strings according to locale-specific rules without manual implementation.

20. Use Array.prototype.flatMap() for mapping and flattening in one step

const sentences = ["Hello world", "How are you"];
const words = sentences.flatMap(sentence => sentence.split(" "));
console.log(words); // ["Hello", "world", "How", "are", "you"]

Why: Combines mapping and flattening operations efficiently, useful for transformations that produce nested results.

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