How to turn off html input form field suggestions?

What you want is to disable HTML autocomplete Attribute.

Setting autocomplete="off" here has two effects:

It stops the browser from saving field data for later autocompletion on similar forms though heuristics that vary by browser. It stops the browser from caching form data in session history. When form data is cached in session history, the information filled in by the user will be visible after the user has submitted the form and clicked on the Back button to go back to the original form page.

Read more on MDN Network

Here's an example how to do it.

<form action="#" autocomplete="on">
  First name:<input type="text" name="fname"><br> 
  Last name: <input type="text" name="lname"><br> 
  E-mail: <input type="email" name="email" autocomplete="off"><br>
  <input type="submit">
</form>

If it's on React framework then use as follows:

<input
    id={field.name}
    className="form-control"
    type="text"
    placeholder={field.name}
    autoComplete="off"
    {...fields}/>

Link to react docs

Update

Here's an update to fix some browsers skipping "autocomplete=off" flag.

<form action="#" autocomplete="off">
  First name: <input type="text" name="fname" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br> Last name: <input type="text" name="lname" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br> E-mail:
  <input type="email" name="email" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br>
  <input type="submit">
</form>

On Chrome, the only method we could identify which prevented all form fills was to use autocomplete="new-password". Apply this on any input which shouldn't have autocomplete, and it'll be enforced (even if the field has nothing to do with passwords, e.g. SomeStateId filling with state form values). See this link on the Chromium bugs discussion for more detail.

Note that this only consistently works on Chromium-based browsers and Safari - Firefox doesn't have special handlers for this new-password (see this discussion for some detail).

Update: Firefox is coming aboard! Nightly v68.0a1 and Beta v67.0b5 (3/27/2019) feature support for the new-password autocomplete attribute, stable releases should be coming on 5/14/2019 per the roadmap.

use autocomplete="off" attribute

Quote:IMPORTANT

Put the attribute on the <input> element, NOT on the <form> element

I know it's been a while but if someone is looking for the answer this might help. I have used autocomplete="new-password" for the password field. and it solved my problem. Here is the MDN documentation.