JSFiddle - React, Tailwind, and code Playground

HTML

<div id=forOutput></div>
<div id=grepOutput></div>

CSS

body {
    font-family: Verdana;
    font-size: 10pt;
}

JavaScript

var words = ['spain', 'road', 'rain', 'plane', 'plain'];


var similar;

similar = [];
for (var i = 0; i < words.length; i++) {
    var word = words[i];
    if (word.indexOf('ai') >= 0)
        similar.push(word);
}

$('#forOutput').text(similar.join());


similar = $.grep(words, function(word, i) {
    return word.indexOf('ai') >= 0;
});

$('#grepOutput').text(similar.join());