JSFiddle - React, Tailwind, and code Playground

HTML

<input type="submit" name="clear" value="Stop Timer" />
<input type="submit" name="reset" value="Restart Timer" />
<span id="count0">0</span>
<input type="submit" name="increment" value="Increment" />
<br />
<input type="submit" name="clear" value="Stop Timer" />
<input type="submit" name="reset" value="Restart Timer" />
<span id="count1">0</span>
<input type="submit" name="increment" value="Increment" />

<br />
<input type="submit" name="clear" value="Stop Timer" />
<input type="submit" name="reset" value="Restart Timer" />
<span id="count2">0</span>
<input type="submit" name="increment" value="Increment" />

<br />
<input type="submit" name="clear" value="Stop Timer" />
<input type="submit" name="reset" value="Restart Timer" />
<span id="count3">0</span>
<input type="submit" name="increment" value="Increment" />

<br />
<input type="submit" name="clear" value="Stop Timer" />
<input type="submit" name="reset" value="Restart Timer" />
<span id="count4">0</span>
<input type="submit" name="increment" value="Increment" />

JavaScript

(function(){ //Anonymous function, to not leak variables to the global scope
        var defaultSpeed = 3000; //Used when missing
        var timerSpeed = [500, 1000, 2000, 4000, 8000];
    
        var intervals = [];
        function increase(i){
            return function(){
                var elem = $("#count"+i);
                elem.text(parseFloat(elem.text()) + 1);
            }
        }
        function clear(i){
            return function(){
                clearInterval(intervals[i]);
            }
        }
        function restart(i){ //Start AND restart
            return function(){
                clear(i)();
                increase(i)();
                intervals[i] = setInterval(increase(i), timerSpeed[i]||defaultSpeed);
            }
        }
        // Manual increment
        $('input[name=increment]').each(function(i){
            $(this).click(function(){
                restart(i)();
                increase(i)();
            });
        });
        
        // Clear timer on "Clear"
        $('input[name=clear]').each(function(i) {
            $(this).click(clear(i));
        });
        
        // Restart timer on "Restart"
        $('input[name=reset]').each(function(i) {
            $(this).click(restart(i));
    
            //Optionally, activate each timer:
            restart(i)();
        });
    })();