我不知道你想做什么，但这应该返回true：

var text = "https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&fmt=jpeg&qlt=80&.v=1603399121000";
const regex = new RegExp(/(\W)(jpg|jpeg|png|gif|webp)(\W)/);
console.log(regex.test(text));

您可以使用此正则表达式测试URL参数fmt=<format>：

• 第一个例子：fmt=jpeg位于中间
• 第二个例子：结束时fmt=jpeg
• 第三个例子：fmt=bmp（不支持的格式）

const regex = /\bfmt=(jpg|jpeg|png|gif|webp)(?=(&|$))/;
[
  'https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&fmt=jpeg&qlt=80&.v=1603399121000',
  'https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&qlt=80&.v=1603399121000&fmt=jpeg',
  'https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&fmt=bmp&qlt=80&.v=1603399121000',
].forEach(url => {
  console.log(url + ' => ' + regex.test(url));
});

输出量：

https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&fmt=jpeg&qlt=80&.v=1603399121000 => true
https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&qlt=80&.v=1603399121000&fmt=jpeg => true
https://store.storeimages.cdn-apple.com/4668/as-images.apple.com/is/macbook-air-gallery3-20201110?wid=4000&hei=3072&fmt=bmp&qlt=80&.v=1603399121000 => false

正则表达式说明：

• \b-字边界
• fmt=-文字fmt=参数（这是为了避免误报）
• (jpg|jpeg|png|gif|webp)-支持的文件扩展名的逻辑“或”
• (?=(&|$))-&或字符串结尾的正前瞻