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JavaScript

var s = "Hello everyone on stackoverflow";

var y = "<html><head><head><body><div>Hello<span>everyone</span>on stackoverflow</div></body></html>";

//using regular expressions match HTML tags and replace them with empty string. Make sure to trim the output so that the extra whitespaces at either end are removed.
var z = y.replace(/(<([^>]+)>)/ig, ' ').trim();

//compare if the stripped string matches the other string.
if(z == s) {
	s = y;  
}
alert(s);