Dennis O'Keeffe

Web Fetch API

Looking at usage of the web "fetch" API. This example uses the node-fetch library for demonstration purposes.

2 min read

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Full disclosure, I normally use axios as my library of choice for http fetching. This is in case I get asked this question in the upcoming interviews and they want me to use a native web API.

Setup

We are going to use Nodejs for this, so just create a file index.js anywhere you want.

The fetch API is promise based, so let's take a look as a basic implementation and then using async/await.

Because we are using node, we need to download the npm package that uses the same API. Let's setup the repo and package with the following:

yarn init -y | yarn add node-fetch

Usage

We will basically run the script as blocking, but syntax-wise we will run through both an await version and standard.

We will use https://postman-echo.com/post as our endpoint to essentially test if we make a successful call and look for the 200 status.

Standard

const fetch = require("node-fetch");
const runFetch = () => {
  const url = "https://postman-echo.com/post";
  const json = {
    foo: "bar",
  };

  return fetch(url, {
    method: "post",
    headers: {
      "Content-type": "application/json",
    },
    body: JSON.stringify(json),
  })
    .then(function (data) {
      console.log("Request succeeded with JSON response", data.status);
    })
    .catch(function (error) {
      console.log("Request failed", error);
    });
};

const run = async () => await runFetch();
run();

If we run node index.js from our CLI we will see Request succeeded with JSON response 200.

Await

const fetch = require("node-fetch");
const runFetch = () => {
  return new Promise((resolve, reject) => {
    const url = "https://postman-echo.com/post";
    const json = {
      foo: "bar",
    };

    try {
      const data = fetch(url, {
        method: "post",
        headers: {
          "Content-type": "application/json",
        },
        body: JSON.stringify(json),
      });
      console.log("Request succeeded with JSON response", data.status);
      resolve();
    } catch (err) {
      console.log("Request failed", error);
      reject();
    }
  });
};

const run = async () => await runFetch();
run();

With this method, we are returning a Promise to begin with but manually running our try/catch block with a resolve/reject resolution based on failure or success.

Reference