使用let关键字是否可行？旧浏览器兼容问题及解决方案咨询

First off, let's tackle your first question clearly: Is using let feasible when most old browsers don't support it?
The short answer is no—not without extra steps. Browsers like IE11 and earlier have zero support for let (and other ES6+ syntax). If you drop untranspiled let into these browsers, you'll hit a syntax error that can completely break your script. So using let straight-up without handling compatibility will absolutely lead to failed runs on older environments.

Now, the second part: Solutions to keep using let without breaking old browsers
Luckily, there are tried-and-true workarounds that let you keep leveraging let's block-scoping benefits while supporting legacy browsers:

• Transpile your code with Babel
  Babel is the go-to tool for converting modern JavaScript (like let, const, arrow functions) into ES5 code that old browsers understand. It’ll turn your let declarations into var (with extra logic to mimic block scoping, so you don’t lose let’s safe behavior). For example, a block-scoped let inside an if statement gets converted to a var wrapped in an IIFE or similar trick to avoid hoisting bugs.

• Use a bundler with built-in transpilation
  Tools like Webpack, Vite, or Parcel integrate seamlessly with Babel (or have their own transpilers). When you set up your project with these tools, they’ll automatically process your code during the build step, outputting browser-compatible files. Just configure your target browsers (e.g., using browserslist to specify "IE 11" if needed) and the bundler handles the rest.

• Skip polyfills for let (they won’t help)
  Remember: let is a syntax feature, not a missing browser API. Polyfills work for adding functions like Array.prototype.includes, but syntax needs to be transformed before it ever hits the browser—polyfills can’t fix a syntax error.

• Lint to catch issues early
  Set up ESLint with rules that flag unsupported syntax if you’re targeting old browsers. This helps catch accidental modern code in development, before you deploy something that breaks production.

If you really can’t use transpilation for some edge case, you could fall back to var—but that’s not ideal. var’s hoisting behavior is a common source of bugs, so it’s worth putting in the small effort to make let work across all your target browsers.

内容的提问来源于stack exchange，提问作者Sourabh Jain 543