Cancelling previous requests in Search bar using Axios in React
Tags: react, javascript
Published: 2020-06-12 14:49:17

#Why do we really need to cancel?
If you are thinking what is the use of canceling? Apart from the obvious reason for saving the resources, there is one more reason: That is, if the response of the first request arrives after the response of the second request, then we might render inconsistent data.

Of course, we can make use of a [debounce value](https://www.codingdeft.com/posts/react-debounce-throttle/). However, if the user types slower than the set debounce value, then it might not help!

{% youtube cIwpavIhI84%}

#The Solution

The solution here is to cancel the previous request. This can be done by storing a reference to the Axios call in a variable and canceling whenever a new request is triggered.

Let's dive in:

#Setup a mock server
For our demonstration let's set up a [json-server](https://github.com/typicode/json-server)
Install the json-server globally. Installing globally because json-server will come handy anytime!

```bash
npm install -g json-server
```

Create a db.json file in the place of your choice with the following JSON data:

```json
{"animals":[{"id":0,"name":"Aardvark"},{"id":1,"name":"Albatross"},{"id":2,"name":"Alligator"},{"id":3,"name":"Alpaca"},{"id":4,"name":"Ant"},{"id":5,"name":"Anteater"},{"id":6,"name":"Antelope"},{"id":7,"name":"Ape"},{"id":8,"name":"Armadillo"},{"id":9,"name":"Donkey"},{"id":10,"name":"Baboon"},{"id":11,"name":"Badger"},{"id":12,"name":"Barracuda"},{"id":13,"name":"Bat"},{"id":14,"name":"Bear"},{"id":15,"name":"Beaver"},{"id":16,"name":"Bee"},{"id":17,"name":"Bison"},{"id":18,"name":"Boar"},{"id":19,"name":"Buffalo"},{"id":20,"name":"Butterfly"},{"id":21,"name":"Camel"},{"id":22,"name":"Capybara"},{"id":23,"name":"Caribou"},{"id":24,"name":"Cassowary"},{"id":25,"name":"Cat"},{"id":26,"name":"Caterpillar"},{"id":27,"name":"Cattle"},{"id":28,"name":"Chamois"},{"id":29,"name":"Cheetah"},{"id":30,"name":"Chicken"},{"id":31,"name":"Chimpanzee"},{"id":32,"name":"Chinchilla"},{"id":33,"name":"Chough"},{"id":34,"name":"Clam"},{"id":35,"name":"Cobra"},{"id":36,"name":"Cockroach"},{"id":37,"name":"Cod"},{"id":38,"name":"Cormorant"},{"id":39,"name":"Coyote"},{"id":40,"name":"Crab"},{"id":41,"name":"Crane"},{"id":42,"name":"Crocodile"},{"id":43,"name":"Crow"},{"id":44,"name":"Curlew"},{"id":45,"name":"Deer"},{"id":46,"name":"Dinosaur"},{"id":47,"name":"Dog"},{"id":48,"name":"Dogfish"},{"id":49,"name":"Dolphin"},{"id":50,"name":"Dotterel"},{"id":51,"name":"Dove"},{"id":52,"name":"Dragonfly"},{"id":53,"name":"Duck"},{"id":54,"name":"Dugong"},{"id":55,"name":"Dunlin"},{"id":56,"name":"Eagle"},{"id":57,"name":"Echidna"},{"id":58,"name":"Eel"},{"id":59,"name":"Eland"},{"id":60,"name":"Elephant"},{"id":61,"name":"Elk"},{"id":62,"name":"Emu"},{"id":63,"name":"Falcon"},{"id":64,"name":"Ferret"},{"id":65,"name":"Finch"},{"id":66,"name":"Fish"},{"id":67,"name":"Flamingo"},{"id":68,"name":"Fly"},{"id":69,"name":"Fox"},{"id":70,"name":"Frog"},{"id":71,"name":"Gaur"},{"id":72,"name":"Gazelle"},{"id":73,"name":"Gerbil"},{"id":74,"name":"Giraffe"},{"id":75,"name":"Gnat"},{"id":76,"name":"Gnu"},{"id":77,"name":"Goat"},{"id":78,"name":"Goldfinch"},{"id":79,"name":"Goldfish"},{"id":80,"name":"Goose"},{"id":81,"name":"Gorilla"},{"id":82,"name":"Goshawk"},{"id":83,"name":"Grasshopper"},{"id":84,"name":"Grouse"},{"id":85,"name":"Guanaco"},{"id":86,"name":"Gull"},{"id":87,"name":"Hamster"},{"id":88,"name":"Hare"},{"id":89,"name":"Hawk"},{"id":90,"name":"Hedgehog"},{"id":91,"name":"Heron"},{"id":92,"name":"Herring"},{"id":93,"name":"Hippopotamus"},{"id":94,"name":"Hornet"},{"id":95,"name":"Horse"},{"id":96,"name":"Human"},{"id":97,"name":"Hummingbird"},{"id":98,"name":"Hyena"},{"id":99,"name":"Ibex"},{"id":100,"name":"Ibis"},{"id":101,"name":"Jackal"},{"id":102,"name":"Jaguar"},{"id":103,"name":"Jay"},{"id":104,"name":"Jellyfish"},{"id":105,"name":"Kangaroo"},{"id":106,"name":"Kingfisher"},{"id":107,"name":"Koala"},{"id":108,"name":"Kookabura"},{"id":109,"name":"Kouprey"},{"id":110,"name":"Kudu"},{"id":111,"name":"Lapwing"},{"id":112,"name":"Lark"},{"id":113,"name":"Lemur"},{"id":114,"name":"Leopard"},{"id":115,"name":"Lion"},{"id":116,"name":"Llama"},{"id":117,"name":"Lobster"},{"id":118,"name":"Locust"},{"id":119,"name":"Loris"},{"id":120,"name":"Louse"},{"id":121,"name":"Lyrebird"},{"id":122,"name":"Magpie"},{"id":123,"name":"Mallard"},{"id":124,"name":"Manatee"},{"id":125,"name":"Mandrill"},{"id":126,"name":"Mantis"},{"id":127,"name":"Marten"},{"id":128,"name":"Meerkat"},{"id":129,"name":"Mink"},{"id":130,"name":"Mole"},{"id":131,"name":"Mongoose"},{"id":132,"name":"Monkey"},{"id":133,"name":"Moose"},{"id":134,"name":"Mosquito"},{"id":135,"name":"Mouse"},{"id":136,"name":"Mule"},{"id":137,"name":"Narwhal"},{"id":138,"name":"Newt"},{"id":139,"name":"Nightingale"},{"id":140,"name":"Octopus"},{"id":141,"name":"Okapi"},{"id":142,"name":"Opossum"},{"id":143,"name":"Oryx"},{"id":144,"name":"Ostrich"},{"id":145,"name":"Otter"},{"id":146,"name":"Owl"},{"id":147,"name":"Oyster"},{"id":148,"name":"Panther"},{"id":149,"name":"Parrot"},{"id":150,"name":"Partridge"},{"id":151,"name":"Peafowl"},{"id":152,"name":"Pelican"},{"id":153,"name":"Penguin"},{"id":154,"name":"Pheasant"},{"id":155,"name":"Pig"},{"id":156,"name":"Pigeon"},{"id":157,"name":"Pony"},{"id":158,"name":"Porcupine"},{"id":159,"name":"Porpoise"},{"id":160,"name":"Quail"},{"id":161,"name":"Quelea"},{"id":162,"name":"Quetzal"},{"id":163,"name":"Rabbit"},{"id":164,"name":"Raccoon"},{"id":165,"name":"Rail"},{"id":166,"name":"Ram"},{"id":167,"name":"Rat"},{"id":168,"name":"Raven"},{"id":169,"name":"Red deer"},{"id":170,"name":"Red panda"},{"id":171,"name":"Reindeer"},{"id":172,"name":"Rhinoceros"},{"id":173,"name":"Rook"},{"id":174,"name":"Salamander"},{"id":175,"name":"Salmon"},{"id":176,"name":"Sand Dollar"},{"id":177,"name":"Sandpiper"},{"id":178,"name":"Sardine"},{"id":179,"name":"Scorpion"},{"id":180,"name":"Seahorse"},{"id":181,"name":"Seal"},{"id":182,"name":"Shark"},{"id":183,"name":"Sheep"},{"id":184,"name":"Shrew"},{"id":185,"name":"Skunk"},{"id":186,"name":"Snail"},{"id":187,"name":"Snake"},{"id":188,"name":"Sparrow"},{"id":189,"name":"Spider"},{"id":190,"name":"Spoonbill"},{"id":191,"name":"Squid"},{"id":192,"name":"Squirrel"},{"id":193,"name":"Starling"},{"id":194,"name":"Stingray"},{"id":195,"name":"Stinkbug"},{"id":196,"name":"Stork"},{"id":197,"name":"Swallow"},{"id":198,"name":"Swan"},{"id":199,"name":"Tapir"},{"id":200,"name":"Tarsier"},{"id":201,"name":"Termite"},{"id":202,"name":"Tiger"},{"id":203,"name":"Toad"},{"id":204,"name":"Trout"},{"id":205,"name":"Turkey"},{"id":206,"name":"Turtle"},{"id":207,"name":"Viper"},{"id":208,"name":"Vulture"},{"id":209,"name":"Wallaby"},{"id":210,"name":"Walrus"},{"id":211,"name":"Wasp"},{"id":212,"name":"Weasel"},{"id":213,"name":"Whale"},{"id":214,"name":"Wildcat"},{"id":215,"name":"Wolf"},{"id":216,"name":"Wolverine"},{"id":217,"name":"Wombat"},{"id":218,"name":"Woodcock"},{"id":219,"name":"Woodpecker"},{"id":220,"name":"Worm"},{"id":221,"name":"Wren"},{"id":222,"name":"Yak"},{"id":223,"name":"Zebra"}]}
```

Navigate to the directory where `db.json` is placed and run the below command:

```bash
json-server -p 4000 db.json --delay 3000
```
+ We are specifying a port here since json-server will use 3000 by default, which we will need for React!
+ A delay of 3 seconds to simulate a slow API, so that we can cancel!

Open the below URL in a browser and you should be able to see the response:

```
http://localhost:4000/animals
```

#Lets Go the Client Side!
Create a new React Project using [CRA](https://create-react-app.dev/docs/getting-started/):
```bash
create-react-app axios-cancel --use-npm
```
Now open the project in your favorite editor and install Axios using the following command:

```bash
npm i axios
```

Update the App.js with the following code:

```jsx
import axios from "axios";
import React from "react";
import "./App.css";

function App() {
  const handleSearchChange = async (e) => {
    const searchTerm = e.target.value;
    const results = await axios.get(
      `http://localhost:4000/animals?q=${searchTerm}`
    );
    console.log("Results for " + searchTerm + ": " + results.data);
  };

  return (
    <div style={{ marginTop: "3em", textAlign: "center" }}>
      <input
        style={{ width: "60%", height: "1.5rem" }}
        type="text"
        placeholder="Search"
        onChange={handleSearchChange}
      />
    </div>
  );
}

export default App;
```
In the above code, we added
* A search bar using an input element
* An `onChange` handler for the input element called `handleSearchChange` which will be triggered every time we enter a text on the search bar.
* And finally, we are calling the API using Axios by passing the search term.

Now if we try searching for *cat* we will see that 3 different calls made and all 3 responses are logged.

![Search Screenshot](https://dev-to-uploads.s3.amazonaws.com/i/uhldt67q1cbz8krgols7.jpg)

We really don't need the previous 2 responses, which we can cancel when the next request is made. 

#The fix!
Update the `handleSearchChange` as below:

```jsx
  let cancelToken;
  const handleSearchChange = async (e) => {
    const searchTerm = e.target.value;

    //Check if there are any previous pending requests
    if (typeof cancelToken != typeof undefined) {
      cancelToken.cancel("Operation canceled due to new request.");
    }

    //Save the cancel token for the current request
    cancelToken = axios.CancelToken.source();

    try {
      const results = await axios.get(
        `http://localhost:4000/animals?q=${searchTerm}`,
        { cancelToken: cancelToken.token } //Pass the cancel token to the current request
      );
      console.log("Results for " + searchTerm + ": ", results.data);
    } catch (error) {
      console.log(error);
    }
  };
```

Note that `cancelToken` is declared outside the function so that the previous token is retained.

Now if we try to search, we could see that previous requests are canceled and the result is logged only once. That's the one for the latest term. Exactly what we wanted!

![Search screenshot](https://dev-to-uploads.s3.amazonaws.com/i/gzf3j3241jw5ydqnnnmp.JPG)

Here is the final code:

```jsx
import axios from "axios";
import React from "react";
import "./App.css";

function App() {
  let cancelToken;
  const handleSearchChange = async (e) => {
    const searchTerm = e.target.value;

    //Check if there are any previous pending requests
    if (typeof cancelToken != typeof undefined) {
      cancelToken.cancel("Operation canceled due to new request.");
    }

    //Save the cancel token for the current request
    cancelToken = axios.CancelToken.source();

    try {
      const results = await axios.get(
        `http://localhost:4000/animals?q=${searchTerm}`,
        { cancelToken: cancelToken.token } //Pass the cancel token to the current request
      );
      console.log("Results for " + searchTerm + ": ", results.data);
    } catch (error) {
      console.log(error);
    }
  };

  return (
    <div style={{ marginTop: "3em", textAlign: "center" }}>
      <input
        style={{ width: "60%", height: "1.5rem" }}
        type="text"
        placeholder="Search"
        onChange={handleSearchChange}
      />
    </div>
  );
}

export default App;

```

Full source code can be downloaded from [github](https://github.com/collegewap/axios-cancel)