最も一般的な JavaScript 文字列メソッドのリスト

let message = "Hello, world!";
console.log(message.length); // Output: 13

let greeting = "Hello";
let name = "Alice";
let fullGreeting = greeting.concat(", ", name, "!");
console.log(fullGreeting); // Output: "Hello, Alice!"

let message = "JavaScript";
console.log(message.charAt(0)); // Output: "J"
console.log(message.charAt(5)); // Output: "S"

let sentence = "The quick brown fox jumps over the lazy dog.";
console.log(sentence.indexOf("quick")); // Output: 4
console.log(sentence.indexOf("dog")); // Output: 37
console.log(sentence.indexOf("lion")); // Output: -1 (not found)

let quote = "To be, or not to be, that is the question.";
console.log(quote.lastIndexOf("be")); // Output: 23
console.log(quote.lastIndexOf("the")); // Output: 33

let fruit = "apple, banana, cherry";
console.log(fruit.slice(0, 5)); // Output: "apple"
console.log(fruit.slice(7, 13)); // Output: "banana"
console.log(fruit.slice(15)); // Output: "cherry"

let text = "Hello, world!";
console.log(text.substring(0, 5)); // Output: "Hello"
console.log(text.substring(7, 12)); // Output: "world"

let message = "The quick brown fox jumps.";
console.log(message.substr(4, 5)); // Output: "quick"
console.log(message.substr(10)); // Output: "brown fox jumps."

let text = "JAVASCRIPT IS AWESOME!";
console.log(text.toLowerCase()); // Output: "javascript is awesome!"

let text = "hello, world!";
console.log(text.toUpperCase()); // Output: "HELLO, WORLD!"

let greeting = "   Hello, world!   ";
console.log(greeting.trim()); // Output: "Hello, world!"

let text = "I like cats. Cats are fluffy.";
console.log(text.replace("cats", "dogs")); // Output: "I like dogs. Cats are fluffy."
console.log(text.replace(/cats/i, "dogs")); // Output: "I like dogs. Cats are fluffy." (case-insensitive)

let csv = "apple,banana,cherry";
let fruits = csv.split(",");
console.log(fruits); // Output: ["apple", "banana", "cherry"]

let message = "The quick brown fox jumps over the lazy dog.";
console.log(message.includes("quick")); // Output: true
console.log(message.includes("tiger")); // Output: false

let greeting = "Hello, world!";
console.log(greeting.startsWith("Hello")); // Output: true
console.log(greeting.startsWith("world")); // Output: false

let filename = "myfile.pdf";
console.log(filename.endsWith(".pdf")); // Output: true
console.log(filename.endsWith(".txt")); // Output: false

let text = "The quick brown fox jumps.";
let pattern = /quick/;
console.log(text.match(pattern)); // Output: ["quick"]

let text = "The quick brown fox jumps.";
let pattern = /brown/;
console.log(text.search(pattern)); // Output: 10

let message = "Hello ";
console.log(message.repeat(3)); // Output: "Hello Hello Hello "

let greeting = "   Hello, world!   ";
console.log(greeting.trimStart()); // Output: "Hello, world!   "

let greeting = "   Hello, world!   ";
console.log(greeting.trimEnd()); // Output: "   Hello, world!"

let number = "42";
console.log(number.padStart(4, "0")); // Output: "0042"

let str = "Hello, world!";
let result = str.splice(7, 5, "everyone");
console.log(result); // Output: "world"
console.log(str); // Output: "Hello, everyone!"

let num = 42;
console.log(num.toString()); // Output: "42"

let str = "JavaScript";
console.log(str.valueOf()); // Output: "JavaScript"

let message = "Hello";
console.log(message.charCodeAt(0)); // Output: 72
console.log(message.charCodeAt(4)); // Output: 111

let emoji = "?";
console.log(emoji.codePointAt(0)); // Output: 128512

let str1 = "café";
let str2 = "cafe\u0301";
console.log(str1.normalize() === str2.normalize()); // Output: true