node.js中的正则表达式让我迷惑不解

const regex = /\d+/; // 匹配一个或多个数字
const str = 'There are 123 apples and 456 oranges.';
const match = str.match(regex); // 返回 ["123"]

const regex = /apples|oranges/g; // 匹配 "apples" 或 "oranges"
const str = 'I like apples and oranges.';
const newStr = str.replace(regex, 'fruits'); // 返回 "I like fruits and fruits."

const regex = /(\d+)-(\w+)/; // 匹配数字-单词格式，并捕获分组
const str = 'The product code is 123-abc.';
const match = str.match(regex); // 返回 ["123-abc", "123", "abc"]

const regex = new RegExp('\\d+', 'g'); // 使用构造函数创建正则表达式对象
const str = 'There are 123 apples and 456 oranges.';
const matches = str.match(regex); // 返回 ["123", "456"]