Lab 18: HTTP GET

Objectives

• Create an API object that loads data from an REST API
• Update a component to use the API object
• Add Pagination

Steps

Create an API object that loads data from an REST API

1. Create the file src\projects\projectAPI.js.

2. Create a projectAPI object and export it from the file.

3. Implement a get method that requires page and limit parameters and sets the default to page = 1 and limit=20. The projects should be sorted by name.

   json-server supports sorting and paging using the following syntax.

   `${url}?_page=${page}&_limit=${limit}&_sort=name`;

   src\projects\projectAPI.js

   import { Project } from "./Project";
   
   const baseUrl = "http://localhost:4000";
   const url = `${baseUrl}/projects`;
   
   function translateStatusToErrorMessage(status) {
     switch (status) {
       case 401:
         return "Please login again.";
       case 403:
         return "You do not have permission to view the project(s).";
       default:
         return "There was an error retrieving the project(s). Please try again.";
     }
   }
   
   function checkStatus(response) {
     if (response.ok) {
       return response;
     } else {
       const httpErrorInfo = {
         status: response.status,
         statusText: response.statusText,
         url: response.url,
       };
       console.log(`log server http error: ${JSON.stringify(httpErrorInfo)}`);
   
       let errorMessage = translateStatusToErrorMessage(httpErrorInfo.status);
       throw new Error(errorMessage);
     }
   }
   
   function parseJSON(response) {
     return response.json();
   }
   
   // eslint-disable-next-line
   function delay(ms) {
     return function (x) {
       return new Promise((resolve) => setTimeout(() => resolve(x), ms));
     };
   }
   
   const projectAPI = {
     get(page = 1, limit = 20) {
       return fetch(`${url}?_page=${page}&_limit=${limit}&_sort=name`)
         .then(delay(600))
         .then(checkStatus)
         .then(parseJSON)
         .then((projects) => {
           return projects.map((p) => {
             return new Project(p);
           });
         })
         .catch((error) => {
           console.log("log client error " + error);
           throw new Error(
             "There was an error retrieving the projects. Please try again."
           );
         });
     },
   };
   
   export { projectAPI };

Update a component to use the API object

1. Open the file src\projects\ProjectsPage.js.

2. Use the useState function to create two additonal state variables loading and error.

   src\projects\ProjectsPage.js

   ...
    function ProjectsPage() {
      const [projects, setProjects] = useState(MOCK_PROJECTS);
   +  const [loading, setLoading] = useState(false);
   +  const [error, setError] = useState(undefined);
   ...
   }

   DO NOT DELETE the file src\projects\MockProjects.js. We will use it in our unit testing.

3. Change the projects state to be an empty array [] (be sure to remove the mock data).

   src\projects\ProjectsPage.js

   - import { Project } from './Project';
   - import { MOCK_PROJECTS } from './MockProjects';
   ...
    function ProjectsPage() {
   -  const [projects, setProjects] = useState(MOCK_PROJECTS);
   +  const [projects, setProjects] = useState([]);
      const [loading, setLoading] = useState(false);
      const [error, setError] = useState(undefined);
   ...
   }
   ...

4. Implement the loading of the data from the API after the intial component render in a useEffect hook. Follow these specifications.

   1. Set state of loading to true
   2. Call the API: projectAPI.get(1).
   3. If successful, set the returned data into the components projects state variable and set the loading state variable to false.
   4. If an error occurs, set the returned error's message error.message to the components error state and loading to false.

   src\projects\ProjectsPage.js

import React, { Fragment, useState,
+ useEffect } from 'react';
+ import { projectAPI } from './projectAPI';

function ProjectsPage() {
  const [projects, setProjects] = useState<Project[]>([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(undefined);

// Approach 1: using promise then
//  useEffect(() => {
//    setLoading(true);
//    projectAPI
//      .get(1)
//      .then((data) => {
//        setError(null);
//        setLoading(false);
//        setProjects(data);
//      })
//      .catch((e) => {
//        setLoading(false);
//        setError(e.message);
//      });
//  }, []);

 // Approach 2: using async/await
+  useEffect(() => {
+    async function loadProjects() {
+      setLoading(true);
+      try {
+        const data = await projectAPI.get(1);
+        setError(null);
+        setProjects(data);
+      } catch (e) {
+        setError(e.message);
+      } finally {
+        setLoading(false);
+      }
+    }
+    loadProjects();
+  }, []);

...
}
...

1. Display the loading indicator below the <ProjectList />. Only display the indicator when loading=true.

   If you want to try it yourself first before looking at the solution code use the HTML snippet below to format the loading indicator.

   <div class="center-page">
     <span class="spinner primary"></span>
     <p>Loading...</p>
   </div>

   src\projects\ProjectsPage.js

   function ProjectsPage() {
     const [projects, setProjects] = useState<Project[]>([]);
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState(undefined);
   
     ...
   
     return (
       <Fragment>
         <h1>Projects</h1>
   
         <ProjectList onSave={saveProject} projects={projects} />
   
   +      {loading && (
   +        <div className="center-page">
   +          <span className="spinner primary"></span>
   +          <p>Loading...</p>
   +        </div>
   +      )}
       </Fragment>
     );
   }
   
   export default ProjectsPage;

2. Add these CSS styles to center the loading indicator on the page.

   src\index.css

   ... //add below existing styles
   
   html,
   body,
   #root,
   .container,
   .center-page {
     height: 100%;
   }
   
   .center-page {
     display: flex;
     justify-content: center;
     align-items: center;
   }

3. Display the error message above the <ProjectList /> using the HTML snippet below. Only display the indicator when error is defined.

   If you want to try it yourself first before looking at the solution code use the HTML snippet below to format the error.

   <div class="row">
     <div class="card large error">
       <section>
         <p>
           <span class="icon-alert inverse "></span>
           {error}
         </p>
       </section>
     </div>
   </div>

   src\projects\ProjectsPage.js

   function ProjectsPage() {
     const [projects, setProjects] = useState<Project[]>([]);
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState(undefined);
   
     ...
   
     return (
     <>
         <h1>Projects</h1>
   
   +      {error && (
   +        <div className="row">
   +          <div className="card large error">
   +            <section>
   +              <p>
   +                <span className="icon-alert inverse "></span>
   +                {error}
   +              </p>
   +            </section>
   +          </div>
   +        </div>
   +      )}
   
         <ProjectList onSave={saveProject} projects={projects} />
   
         {loading && (
           <div className="center-page">
             <span className="spinner primary"></span>
             <p>Loading...</p>
           </div>
         )}
       </>
     );
   }
   
   export default ProjectsPage;

4. Verify the application is working by following these steps in your Chrome browser.

   1. Open the application on http://localhost:3000.

   2. Open Chrome DevTools.

   3. Refresh the page.

   4. For a brief second, a loading indicator should appear.

   5. Then, a list of projects should appear.

   6. Click on the Chrome DevTools Network tab.

   7. Verify the request to /projects?_page=1&_limit=20&_sort=name is happening.

   8. We are using a delay function in projectAPI.get() to delay the returning of data so it is easier to see the loading indicator. You can remove the delay at this point.

      src\projects\projectAPI.js

      return fetch(`${url}?_page=${page}&_limit=${limit}&_sort=name`)
      - .then(delay(600))
        .then(checkStatus)
        .then(parseJSON);

   9. Change the URL so the API endpoint cannot be reached.

      src\projects\projectAPI.js

      const baseUrl = 'http://localhost:4000';
      - const url = `${baseUrl}/projects`;
      + const url = `${baseUrl}/fail`;
      ...

   10. In your browser, you should see the following error message displayed.

   11. Fix the URL to the backend API before continuing to the next lab.

       src\projects\projectAPI.js

       ...
       const baseUrl = 'http://localhost:4000';
       + const url = `${baseUrl}/projects`;
       - const url = `${baseUrl}/fail`;
       ...

Add Pagination

1. Use the useState function to create an additonal state variable currentPage.

   src\projects\ProjectsPage.js

   ...
   function ProjectsPage() {
     const [projects, setProjects] = useState([]);
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState(undefined);
   + const [currentPage, setCurrentPage] = useState(1);
     ...
   }

2. Update the useEffect method to make currentPage a dependency and use it when fetching the data.

   src\projects\ProjectsPage.js

...
function ProjectsPage() {
  const [projects, setProjects] = useState([]);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(undefined);
  const [currentPage, setCurrentPage] = useState(1);

  useEffect(() => {
    async function loadProjects() {
      setLoading(true);
      try {
-        const data = await projectAPI.get(1);
+        const data = await projectAPI.get(currentPage);
-        setProjects(data);
+      if (currentPage === 1) {
+          setProjects(data);
+        } else {
+          setProjects((projects) => [...projects, ...data]);
+        }
      } catch (e) {
        setError(e.message);
      } finally {
        setLoading(false);
      }
    }
    loadProjects();
-  }, []);
+  }, [currentPage]);
...
}

1. Implement a handleMoreClick event handler and implement it by incrementing the page and then calling loadProjects.

   src\projects\ProjectsPage.js

   ...
   function ProjectsPage() {
     ...
     const [currentPage, setCurrentPage] = useState(1);
     ...
   
   +  const handleMoreClick = () => {
   +    setCurrentPage((currentPage) => currentPage + 1);
   +  };
     ...
   }

2. Add a More... button below the <ProjectList /> . Display the More... button only when not loading and there is not an error and handle the More... button's click event and call handleMoreClick.

   src\projects\ProjectsPage.js

   ...
   function ProjectsPage() {
   ...
   
     return (
       <Fragment>
         <h1>Projects</h1>
         {error && (
           <div className="row">
             <div className="card large error">
               <section>
                 <p>
                   <span className="icon-alert inverse "></span>
                   {error}
                 </p>
               </section>
             </div>
           </div>
         )}
         <ProjectList onSave={saveProject} projects={projects} />
   
   +      {!loading && !error && (
   +        <div className="row">
   +          <div className="col-sm-12">
   +            <div className="button-group fluid">
   +              <button className="button default" onClick={handleMoreClick}>
   +                More...
   +              </button>
   +            </div>
   +          </div>
   +        </div>
   +      )}
   
         {loading && (
           <div className="center-page">
             <span className="spinner primary"></span>
             <p>Loading...</p>
           </div>
         )}
       </Fragment>
     );
   }
   
   export default ProjectsPage;

3. Verify the application is working by following these steps in your browser.

   1. Refresh the page.
   2. A list of projects should appear.
   3. Click on the More... button.
   4. Verify that 20 additional projects are appended to the end of the list.
   5. Click on the More... button again.
   6. Verify that another 20 projects are appended to the end of the list.

   

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✔ You have completed the Lab 18