JSFiddle - React, Tailwind, and code Playground

HTML

<div id="input"></div>
<hr>
<div id="output"></div>

JavaScript

var text='<html><head><meta></hea{"key":"value"}d><body>{"key":0}</body></html>';

var results = [];

for(var start=0; start<text.length; start++){
    for(var end=start+1; end<text.length; end++){
		var part = text.substring(start, end);
		try{
			var json = JSON.parse(part);
			if( typeof json === "object" && !Array.isArray(json) )
				results.push({
					position: start,
        	length: part.length,
					text: part,
					object: json
				});
			start=end+1;
			break;

		}
		catch(err){
			
		}
    }
}

document.getElementById("input").innerText = text;
document.getElementById("output").innerText = JSON.stringify(results, null, '⁣⁣⁣  ');