Use eslint in the browser
import * as eslint from "eslint-linter-browserify";
// or const eslint = require("eslint-linter-browserify");
// or <script src="https://cdn.jsdelivr.net/npm/eslint-linter-browserify/linter.js"></script>
// or <script src="https://cdn.jsdelivr.net/npm/eslint-linter-browserify/linter.min.js"></script>
const linter = new eslint.Linter();
const messages = linter.verify("var foo;", {
rules: {
semi: ["error", "never"]
}
}, { filename: "foo.js" });
console.log(messages);
https://eslint.org/docs/developer-guide/nodejs-api#linter
See the CodeMirror example for a way to use this in CodeMirror.