JavaScript: Add an event listener to an element with the ability to use event delegation

JavaScript fundamental (ES6 Syntax): Exercise-95 with Solution

Write a JavaScript program to add an event listener to an element with the ability to use event delegation.

• Use EventTarget.addEventListener() to add an event listener to an element.
• If there is a target property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this context.
• Omit opts to default to non-delegation behavior and event bubbling.
• Returns a reference to the custom delegator function, in order to be possible to use with off.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const on = (el, evt, fn, opts = {}) => {
  const delegatorFn = e => e.target.matches(opts.target) && fn.call(e.target, e);
  el.addEventListener(evt, opts.target ? delegatorFn : fn, opts.options || false);
  if (opts.target) return delegatorFn;
};

const fn = () => console.log('!');
console.log(on(document.body, 'click', fn));  
console.log(on(document.body, 'click', fn, { target: 'p' }));  
console.log(on(document.body, 'click', fn, { options: true }));

Sample Output:

undefined
undefined
undefined

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-95-1 by w3resource (@w3resource) on CodePen.

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