Test if a String Matches a JavaScript Regular Expression—SitePoint

In this short tutorial on JavaScript regular expression matching, learn how to test whether a string matches a regular expression. test() Method.

Strings are text that can contain various data such as URLs, phone numbers, names, numbers, etc. We often need to check if a string contains text or a certain type of character.

When testing if a string contains a particular substring, you might tend to use something like indexOf()However, it is recommended to use regular expressions for more flexible tests and conditions.

JavaScript regular expression matching allows you to check if a string contains a particular pattern, substring, or character type. Regular expressions are useful for finding information in strings that can be written in a variety of formats, such as dates.

Testing strings against regular expressions

To test whether a string matches a regular expression, we first need to create a regular expression instance.Then you can use test() A method available with regular expressions to check if a string matches a regular expression.

of test() The method accepts one parameter, a string to test against the pattern. Returns a Boolean value indicating whether the string matches the regular expression.

for example:

const pattern = /test.*regular/;
const str = 'I want to test this string against a regular expression';
if (pattern.test(str)) {
  console.log('Matched');
} else {
  console.log('Not Matched');
}

In this example we create a pattern test.*regular. This pattern means that the string must contain the word test and regular These words can be separated by zero or more arbitrary characters.

If test() returns true and Matched logged to the console. Otherwise, Not Matched logged to the console.

ever since str contains the word test and regularand test preceding regular In strings it matches against a pattern and test() Returns true.

You can also declare patterns using the RegExp constructor.

const pattern = new RegExp('test.*regular');
const str = 'I want to test this string against a regular expression';
if (pattern.test(str)) {
  console.log('Matched');
} else {
  console.log('Not Matched');
}

You can test this with the following CodePen demo.

look at the pen
Testing strings against regular expressions with SitePoint (@SitePoint)
with a code pen.

common example

This section provides some examples of how to test common use cases using JavaScript regular expression matching. Note that regular expressions here are not a perfect solution in any case. Each of them is used to give a simple example of how the process works.

URL test

You can use regular expressions to test if a string is a URL. You can try this out using the following CodePen demo.

look at the pen
Tests if a String is a JavaScript URL by SitePoint (@SitePoint).
with a code pen.

The regular expression pattern used above ensures that the URL is http:// again https://.

email test

You can use regular expressions to test whether a string is a valid email address. The following CodePen demo shows how to do it.

look at the pen
Test is a String is an Email in JS by SitePoint (@SitePoint)
with a code pen.

test day

You can use regular expressions to test if a string is a date. The following CodePen demo shows how to do it.

look at the pen
Test with SitePoint (@SitePoint) if a string is a JavaScript date.
with a code pen.

Note that the regex pattern above expects the date to be in the format “DD-MM-YYYY” or “DD/MM/YYYY”.

Other Ways of JavaScript Regular Expression Matching

There are other ways to test whether a string matches a regular expression. We won’t cover everything in this article, but here’s a quick overview:

• match. This method can be used with strings. It accepts a regular expression as a parameter and retrieves the part of the string that matches the regular expression, if any.
• search. This method can be used with strings. Accepts a regular expression as a parameter, searches if a regular expression pattern exists within a string, and if so retrieves the index of the first occurrence of the pattern within the string.
• Executive. This method can be used with regular expressions. It accepts a string as a parameter, searches for a regex pattern within the string, and retrieves the result if it exists.

Conclusion

Regular expressions are very useful for testing if a string contains a certain pattern or substring. JavaScript regular expression matching can be used to check if a string is a URL, date, IP address, or any other type or format.

Compared to using other methods such as indexOf(), test() Using the methods available in regular expressions gives you more flexibility when testing whether a string matches a pattern.

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