//Searching for a substring
let str = 'Widget with id';
// 0, because 'Widget' is found at the beginning
document.getElementById("result").innerHTML = "<i>0, because 'Widget' is found at the beginning:</i> ";
document.getElementById("result").innerHTML += str.indexOf('Widget');
document.getElementById("result").innerHTML += '<br />';
document.getElementById("result").innerHTML += str.indexOf('widget');
document.getElementById("result").innerHTML += '<br />';
document.getElementById("result").innerHTML += str.indexOf("id");
document.getElementById("result").innerHTML += '<br />';
document.getElementById("result").innerHTML += str.indexOf('id', 2);
<h1>String</h1>
<h2>Searching for a substring</h2>
<blockquote>
'Widget with id'
<br />
result:<br />
<span id="result"></span>
</blockquote>