[Regular Expressions] Introduction

var str = "Is this This?";

//var regex = new RegExp("is", "gi");
var regex = /is/gi;

//console.log(regex.test(str));
console.log(regex.exec(str)); //["Is", index: 0, input: "Is this This?"]
console.log(regex.exec(str)); //["is", index: 5, input: "Is this This?"]
console.log(regex.exec(str)); //["is", index: 10, input: "Is this This?"]
console.log(regex.exec(str)); //null

console.log(str.match(regex)); //["Is", "is", "is"]

console.log(str.replace(regex, "XX")); //"XX thXX ThXX?"

console.log(str.search(regex)); // 0, return the first index that found

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App:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Javascript Regular Expressions: Introduction</title>
  <style>
    pre {
      line-height: 2;
    }

    span {
      background-color: #eee;
      padding: 1px;
      outline: 1px solid #999;
    }

  </style>
</head>
<body>
  <pre></pre>
</body>
</html>

'use strict';

const output = (str, regex, target) => {
  target.innerHTML =
    str.replace(regex, str => `<span>${str}</span>`);
}

var str = `Is this This?`;

//var regex = new RegExp("is", "g");
var regex = /is/gi;

output(str, regex, document.querySelector('pre'))

// console.log(regex.test(str));
// console.log(regex.exec(str));
// console.log(regex.exec(str));
// console.log(regex.exec(str));
// console.log(regex.exec(str));
// console.log(str.match(regex));
// console.log(str.replace(regex, str => "XX"));
// console.log(str.search(regex));