square-brackets.js

/***
 * Dynamic Object properties using square brackets
 */
let beverage = 'Beer';

const myObj = {
  a: 1,
  b: 2,
  c: 3,
  food: 'cheese',
  propName: 'cheese',
  beverage: 'Heineken', // beverage: 'Heineken'
  [beverage]: 'corona', // Beer: 'corona'
};

let addProp = (obj, propName, propValue) => {
  // obj.food = 'cheese';
  obj[propName] = propValue;
  obj.propName = propValue;
};
addProp(myObj, 'food', 'cheese');

Amazing square brakets: it's working even in:

myFunction(id) {
let element = document.getElementById([id]);
}

Amazing square brackets: it's working even in:

myFunction(id) {
let element = document.getElementById([id]);
}

They are cool. Your example would also work without the square brackets. The variable would be evaluated inside the ( ) because there are no quotation marks.