<a href="#" onclick="addP(); this.onclick='';">See more</a>    
Why does the function run once when I put this.onclick=' ';?
<a href="#" onclick="addP(); this.onclick='';">See more</a>    
Why does the function run once when I put this.onclick=' ';?
When you clicked the link.
addP.Now the actual HTML looks like
<a href="#" onclick="addP();">See more</a> 
To fix this remove onclick='' part in the onclick attribute.
let addP = () => alert('you clicked the link')<a href="#" onclick="addP();">See more</a>     
    
    You have to remove this.onclick=''; because when the o'clock event (addP) Is over, it removes the the click event handler. So there are 2 methods for you :
Method 1
use javascript & html like so :
HTML :
<a href="#" id="seeMore">See more</a>    
Javascript :
document.getElementById('seeMore').addEventListener('click', function() {
    addP();
});
Method 2
only using html
<a href="#" onclick="addP();">See more</a>    
