An example of JS substr with negative index

JavaScript / HTML/ CSS Code

Output

<!DOCTYPE html>
<html>
<head>


<style>
.substrdiv {
  background: #D9524E;
  height: auto;
  width:300px;
  border-radius: 15px;
  padding:20px;
  font-size:16px;
  color:#fff;  
}
#substr {
    background: #4E6576;
}
.paracls {
    background: #4E6576;
}
.btncls{
    background-color:#5ABFDD;
    border: #2e6da4;
  	font-family: Arial, Geneva, Arial, Helvetica,  sans-serif;
	font-size: 15px;
    color: #FFFFFF;
    letter-spacing: 1px;
    padding: 8px 12px;
    font-size: 14px;
    font-weight: normal;

    border-radius: 4px;
    line-height: 1.5;
    text-decoration:none;
} 
</style>
</head>

<body>
<div class="substrdiv">Main String: "The JavaScript substr tutorial!" 
<p class="paracls">var str_sub = source_string.substr(-10, 17);</p>
<p>After substr method: <span id="substr"></span></p>

</div>

<p><button class="btncls" onclick="getsubstring()">Execute substr method</button></p>
<script type="text/javascript">
function getsubstring(){
var source_string = ("The JavaScript substr tutorial!");
var str_sub = source_string.substr(-10, 17);

document.getElementById("substr").innerHTML = str_sub;
}
</script>
</body>
</html>

Main String: "The JavaScript substr tutorial!"

var str_sub = source_string.substr(-10, 17);

After substr method: