该应用程序缺少渲染路由器以提供路由上下文和history对象。
导入路由器并 Package App组件。
示例：

import { StrictMode } from "react";
import { createRoot } from "react-dom/client";
import { BrowserRouter } from "react-router-dom";
import App from "./App";

const rootElement = document.getElementById("root");
const root = createRoot(rootElement);

root.render(
  <StrictMode>
    <BrowserRouter>
      <App />
    </BrowserRouter>
  </StrictMode>
);

由于您正在使用react@18并将应用渲染到React.StrictMode组件中，因此您还需要至少***转换到***react-router-dom@5.3.3以解析compatibility issue between React 18 and RRDv5。
Login组件还应导航到应用正在呈现路由的路径。history.push("./components/JobFindPage");将错误地将"/components/JobFindPage"附加到当前URL路径的末尾。

import React, { useState } from "react";
import { useHistory } from "react-router-dom";

export default function LoginPage() {
  const history = useHistory();

  //set the initial sate for the inputs
  const [username, setusername] = useState("");
  const [password, setpassword] = useState("");

  //function to handle form submission
  const handleFormSubmit = (event) => {
    event.preventDefault(); // prevent from refreshing the page

    //checck the user name and password
    if (username === "employee" && password === "emp123") {
      history.push("/JobFindPage"); // <-- fix this path
      alert("hii");
    } else if (username === "employer" && password === "emr123") {
      history.push("/CreateJobPage");
      alert("hii");
    } else {
      alert("wrong username or password");
    }
  };

  return (
    <>
      <form onSubmit={handleFormSubmit}>
        <label>
          Username :
          <input
            type="text"
            value={username}
            onChange={(e) => setusername(e.target.value)}
          />{" "}
          <br />
        </label>
        <label>
          Password :
          <input
            type="text"
            value={password}
            onChange={(e) => setpassword(e.target.value)}
          />{" "}
          <br />
        </label>
        <button type="submit">Log IN</button>
      </form>
    </>
  );
}