js对字符串处理

let str1 = 'hello';
let str2 = "world";
let str3 = `Hello, ${str2}!`; // 使用模板字符串

let str = "Hello, world!";
let index = str.indexOf("world"); // 返回7

let str = "Hello, world!";
let newStr = str.replace("world", "everyone"); // "Hello, everyone!"

let str = "apple, banana, cherry";
let fruits = str.split(", "); // ["apple", "banana", "cherry"]

let str1 = "Hello, ";
let str2 = "world!";
let greeting = str1 + str2; // "Hello, world!"
// 或者使用concat()
let greeting2 = str1.concat(str2);

let str = "Hello, world!";
let upperStr = str.toUpperCase(); // "HELLO, WORLD!"
let lowerStr = str.toLowerCase(); // "hello, world!"

let str = "   Hello, world!   ";
let trimmedStr = str.trim(); // "Hello, world!"

let str = "Hello, world!";
let hasWorld = str.includes("world"); // true

function countCharacters(str) {
    let charCount = {};
    for (let char of str) {
        if (charCount[char]) {
            charCount[char]++;
        } else {
            charCount[char] = 1;
        }
    }
    return charCount;
}

let result = countCharacters("hello");
console.log(result); // { h: 1, e: 1, l: 2, o: 1 }