Javascript print triangle doesn't work as expected

Try to clear your text in the outer for loop,

for(var i=1;i<=n;i++){
    text = "";

Full code would be,

function show(n){
 var text;
 for(var i=1;i<=n;i++){
    text = "";
    for(var j=1;j<=i;j++){
        text+='#';
    }
    console.log(text);
 }
}
show(4);

You don't need two loops for that. Just append one character in each iteration and print it out:

var text = "";

for(var i=0; i < n; i++){ 
 text += "#";
 console.log(text); 
}

//prints for n=8: 

#
##
###
####
#####
######
#######
########

You can do loop this way:

<div id="result"></div>
<script>
function show(n){
    var text = "";
    for(var i=1;i<=n;i++){
        for(var j=1;j<=i;j++){
          text+='#';
        }
        text+="<br/>";
        document.getElementById('result').innerHTML = text;
    }
}
show(4);
</script>

Your Output