replacement.js

var itens = [
  'apple',
  'grape',
  'orange'
];

itens
  .join(',')
  .replace(/(\w+(?!=\,))/g, '<li>\$1<\li>')
  .split(',');
  
// [ '<li>apple<\li>', '<li>grape<\li>', '<li>orange</li>' ]

Teimoso!!!
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

var i = 0, itens = ['foo', 'bar', 'baz'];
while (itens[i]) {
    itens[i] = '<li>' + itens[i] + '</li>';
    i += 1;
}

ˆ ˆ

Outro modo de se fazer :-)

var itens = [
  'apple',
  'grape',
  'orange'
];

function list(word) {
    return '<li>' + word + '</li>';
}

itens.map(list);