substring的用法js

let str = "Hello, World!";

// 提取 "Hello"
let result1 = str.substring(0, 5);
console.log(result1); // 输出: Hello

// 提取 "World"
let result2 = str.substring(7);
console.log(result2); // 输出: World!

// 提取整个字符串
let result3 = str.substring(0);
console.log(result3); // 输出: Hello, World!

let str = "Hello";
let result = str.substring(10, 20);
console.log(result); // 输出: 空字符串，因为索引超出范围

let str = "Hello";
let startIndex = 10;
let endIndex = 20;

if (startIndex < str.length && endIndex <= str.length) {
    let result = str.substring(startIndex, endIndex);
    console.log(result);
} else {
    console.log("索引超出范围");
}

let str = "Hello";
let result = str.substring(-3, 2);
console.log(result); // 输出: He

let str = "Hello";
let startIndex = -3;
let endIndex = 2;

if (startIndex < 0) startIndex = 0;
if (endIndex < 0) endIndex = 0;

let result = str.substring(startIndex, endIndex);
console.log(result); // 输出: He