To fetch data from http://wikipedia.org:

fetch(`https://api.allorigins.win/get?url=${encodeURIComponent('https://wikipedia.org')}`)
                    .then(response => {
                      if (response.ok) return response.json()
                      throw new Error('Network response was not ok.')
                    })
                    .then(data => console.log(data.contents));
                  

Or with jQuery

$.getJSON('https://api.allorigins.win/get?url=' + encodeURIComponent('https://wikipedia.org'), function (data) {
                      alert(data.contents);
                  });