RegExp Methods # 02

Regular Expression Methods

Test() method

JavaScript has multiple ways to use regexes. One way to test a regex is using the .test() method. The .test() method takes the regex, applies it to a string (which is placed inside the parentheses), and returns true or false if your pattern finds something or not.

var stringText = "Mozahedul Islam is a good man and a programmer.";
var pattern = /good/;

/* test() method find the match between a regular 
expression and a specified string.return a boolean value. 
If it finds the match, then returns true. 
Otherwise returns false.
 */

var matchItem = pattern.test(stringText);
console.log(matchItem);
// return: true

exec() method

The exec() method executes a search for a match in a specified string and if any match is found, then returns a result array, or not found then returns null.

var stringText =
  'Mozahedul Islam is a good man and a programmer. He is also good in mathematics';
var pattern = new RegExp('good', 'g');
 
var matchItem = pattern.exec(stringText);
console.log(matchItem);
// return
0: "good"
groups: undefined
index: 21
input: "Mozahedul Islam is a good man and a programmer. He is also good in mathematics"
length: 1
[[Prototype]]: Array(0)

If we use the exec() method normally, then it will return only the first matching character or word. For this, we have to use this method within a loop like the below…

const str =
  'Mozahedul Islam is a good and famous programmer. He is not only a good programmer but also a good human being.';
const reg = new RegExp('good', 'g');
 
var result = '';
let arr;
while ((arr = reg.exec(str)) !== null) {
  // Reason for using arr[0];
  // reg.exec() method will return an array
  // this array contains the matching character or word
  // as the first array item
  result += `${arr[0]} with index number ${reg.lastIndex}\n`;
  console.log(arr);
}

document.getElementById('regex').innerText = result;

---