Как узнать, какой элемент вызвал функцию?

btn1.addEventListener('click', handler) 
btn2.addEventListener('click', handler) 
 
function handler(e) { 
 console.log("this =", this) 
 console.log("e.target =", e.target) 
}

<button id="btn1">btn 1</button> 
<button id="btn2">btn 2</button>

function handler() { 
 console.log("this =", this) 
}

<button onclick="handler.apply(this)">btn 1</button> 
<button onclick="handler.apply(this)">btn 2</button>

function someFunction(id, value) { 
  console.log(id, value); 
}

<input type="range" oninput="someFunction(1, this.value)" /> 
<input type="range" oninput="someFunction(2, this.value)" />