how to call different methods of any function in javascript code example

Example 1: javascript function call with variable

function abc() {
  alert('test');
}

var funcName = 'abc';

window[funcName]();

Example 2: how do i call a js method?

<button onclick="sayHello()">say hello</button>  <script>    'use strict';  //force the context to be undefined    function sayHello() {      console.log(this);      console.log(arguments);      console.log('hello');    }  </script>