innerHTML not working with classname in JS

Answer 1

document.getElementsByClassName("catlink")is selecting all the elements in webpage as array therefore you have to use [0]

 function showDiv( discselect ) 
 { 

 if( discselect === 1) 
 { 
 alert(discselect); // This is alerting fine 
 document.getElementsByClassName("catlink")[0].innerHTML = "aaaaaaqwerty"; // Now working 
 } 
 }