How to implement autocompletion in a JavaScript application?

Implementing autocomplete in a JavaScript application typically involves the following steps:

1. Create an input box for the user to start typing the desired keyword or query.

```

1. Create a list of predetermined keywords, phrases, or queries that can be used for autocompletion. This can typically be stored in an array. In a more advanced implementation, these keywords could be fetched from an online source or API.

```
let autoCompleteList = [“Apple”, “Banana”, “Cherry”, “Date”, “Elderberry”, “Fig”, “Grape”];
```

1. Implement a function to process user typing events. In this function, compare the text that the user has currently entered into the input box with your list of predetermined keywords.

```
function autocomplete() { let input = document.getElementById(‘search’).value; document.getElementById(‘suggestions’).innerHTML = “”;

for (let i = 0; i < autoCompleteList.length; i++) { if (autoCompleteList[i].toLowerCase().startsWith(input.toLowerCase())) { let node = document.createElement(‘div’); node.innerText = autoCompleteList[i]; node.onclick = function() { document.getElementById(‘search’).value = node.innerText; } document.getElementById(‘suggestions’).appendChild(node); } } } ```

This code will produce suggestions that match the start of the user’s input. Clicking on a suggestion will fill the input box with that suggestion.

Of course, how you implement autocomplete will depend on the specifics of your application. Rendering, selecting, and using autocomplete suggestions can be quite sophisticated.

For example, you might want to use an external library like jQuery UI’s Autocomplete or Typeahead.js which provide more advanced features out of the box, like fetching suggestions from a server, highlighting, keyboard navigation, etc.

In a React application, you might want to include stateful logic for managing user input and selection among suggestions, and use components to render the autocomplete suggestions.

There are also services and APIs that provide autocomplete functionality for specific types of content. For example, the Google Maps Places API provides a way to implement autocomplete for location names.