A mobile website can be customized to allow users to share a pre-filled message in WhatsApp to a manually chosen contact. As given here it is done using Custom URL Scheme. A
Format to send a WhatsApp message to a specific number (updated Nov 2018)
<a href="https://wa.me/whatsappphonenumber/?text=urlencodedtext"></a>
where
whatsappphonenumber is a full phone number in international format
urlencodedtext is the URL-encoded pre-filled message.
Create a link with a pre-filled message that will automatically appear in the text field of a chat, to be sent to a specific number
Send I am interested in your car for sale to +001-(555)1234567
https://wa.me/15551234567?text=I%20am%20interested%20in%20your%20car%20for%20sale
Note :
Use: https://wa.me/15551234567
Don't use: https://wa.me/+001-(555)1234567
Create a link with just a pre-filled message that will automatically appear in the text field of a chat, number will be chosen by the user
Send I am enquiring about the apartment listing
https://wa.me/?text=I%20am%20enquiring%20about%20the%20apartment%20listing
After clicking on the link, user will be shown a list of contacts they can send the pre-filled message to.
For more information, see https://www.whatsapp.com/faq/en/general/26000030
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P.S : Older format (before updation) for reference
<a href="https://api.whatsapp.com/send?phone=whatsappphonenumber&text=urlencodedtext"></a>
This answer is useful to them who want click to chat whatsapp in website to redirect web.whatsapp.com with default content or message and in mobile device to open in whatsapp in mobile app with default content to text bar in app.
also add jquery link.
<a target="_blank" title="Contact Us On WhatsApp" href="https://web.whatsapp.com/send?phone=+91xxxxxxxxx&text=Hi, I would like to get more information.." class="whatsapplink hidemobile" style="background-color:#2DC100">
<i class="fa fa-fw fa-whatsapp" style="color:#fff"></i>
<span style="color:#fff">
Contact Us On WhatsApp </span>
</a>
<a target="_blank" title="Contact Us On WhatsApp" href="https://api.whatsapp.com/send?phone=+91xxxxxxxxx&text=Hi,%20I%20would%20like%20to%20get%20more%20information.." class="whatsapplink hideweb" style="background-color:#2DC100">
<i class="fa fa-fw fa-whatsapp" style="color:#fff"></i>
<span style="color:#fff">
Contact Us On WhatsApp </span>
</a>
<script type="text/javascript">
var mobile = (/iphone|ipod|android|blackberry|mini|windows\sce|palm/i.test(navigator.userAgent.toLowerCase()));
if (mobile) {
$('.hidemobile').css('display', 'none'); // OR you can use $('.hidemobile').hide();
}
else
{
$('.hideweb').css('display', 'none'); // OR you can use $('.hideweb').hide();
}
</script>
To send a Whatsapp message from a website, use the below URL.
URL: https://api.whatsapp.com/send?phone=XXXXX&text=dummy
Here the phone and text are parameters were one of them is required.
This URL is also can be used. It displays a blank screen if there is no application found!
URL: whatsapp://send?text=The text to share!
Note: All the above will work in web, only if WhatsApp desktop app is installed