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Javascript Regular Expressions
Javascript Regular Expressions

Javascript Regular Expressions: Leverage the power of regular expressions to create an engaging user experience

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Profile Icon Loiane Groner Profile Icon Gabriel Manricks
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Full star icon Full star icon Full star icon Full star icon Empty star icon 4 (7 Ratings)
Paperback May 2015 112 pages 1st Edition
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Arrow left icon
Profile Icon Loiane Groner Profile Icon Gabriel Manricks
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Paperback May 2015 112 pages 1st Edition
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Javascript Regular Expressions

Chapter 2. The Basics

In the previous chapter, we have already seen that in order to match a substring, you simply need to write the string inside a regular expression. For example, to match hello, you would create this variable:

var pattern = /hello/;

We also learned that if we want to match all occurrences of the string or character of the regular expression, we can use the g flag within Regex. However, situations where you have as clear a pattern like these are rare, and even when they come up, it's arguable whether Regex is even required. You really see the true power of regular expressions when you have less concrete information.

There are two main features the Regex engine implements that allow you to correctly represent 80 percent of your patterns. We will cover these two main features in this chapter:

  • Vague matchers
  • Multipliers

Defining vague matchers in Regex

In this topic, we will cover character classes that tell the Regex to match a single vague character. Among the vague matches, there can be a character, digit, or an alphanumeric character.

Matching a wild card character

Let's say we wanted to find a sequence where we have 1, and then any other character followed by 3, so that it would include 123, 1b3, 1 3, 133, and so on. For these types of situations, we need to use a vague matcher in our patterns.

In the preceding example, we want to be able to use the broadest matcher possible; we can choose to put no constraints on it if we wish to and it can include any character. For these kind of situations, we have the . matcher.

A period in Regex will match any character except a new line, so it can include letters, numbers, symbols, and so on. To test this out, let's implement the aforementioned example in our HTML utility. In the text field, let's enter a few combinations to test the pattern against...

Defining ranges in Regex

Ranges in Regex allow you to create your own custom constraints, much like the ones we just went through. In a range, you can specify exactly the characters that can be used or if it's faster, you can specify the inverse, that is, the characters that do not match.

For the sake of illustration, let's say we wanted to match only abc. In this case, we could create a range similar to [abc] and it will match a single character, which is either a, b, or c. Let's test it out with the bicycle text and the /[abc]/g pattern:

Defining ranges in Regex

Defining a range

Now, this will work, however, if you have a lot of characters you need to match, your range will become long quickly. Luckily, Regex allows you to use the (-) dash character to specify a set of characters without needing to list them out. For example, let's say we want to check whether a three lettered name is formatted correctly, and we want the first letter to be a capital letter, followed by two lower case letters...

Defining multipliers in Regex

Matchers are great but they only "scale" your pattern in one direction. I like to think of matchers as things that scale your pattern vertically, allowing you to match many more strings that fit into the same pattern, but they are still constrained in length, or scale the pattern horizontally. Multipliers allow you to match arbitrarily sized strings that you may receive as input, giving you a much greater range of freedom.

There are three basic multipliers in Regex:

  • +: This matches one or more occurrences
  • ?: This matches zero or one occurrence
  • *: This matches zero or more occurrences

We will cover these three multipliers in this section, and also show you how to create a custom multiplier.

Matching one or more occurrences

The most basic multiplier would have to be the (+) plus operator. It tells JavaScript that the pattern used in the regular expression must appear one or more times. For example, we can build upon the formatted name pattern we used before...

Defining custom quantifiers

There is only one syntax to specify your own multipliers but because of the different parameter options available, you get three different functional options.

If you want to match a given character a concrete number of times, you can simply specify the number of allowed repetitions inside curly braces. This doesn't make your patterns more flexible, but it will make them shorter to read. For example, if we were implementing a phone number we could type /\d\d\d-\d\d\d\d/. This is, however, a bit long and instead, we can just use custom multipliers and type /\d{3}-\d{4}/, which really shorten it up making it more readable.

Matching n or more occurrences

Next, if you just want to set a minimum number of times that the pattern can appear, but don't really care about the actual length, you can just add a comma after the number. For example, let's say we want to create a pattern to make sure a user's password is at least six characters long; in such...

Matching alternated options

At this stage, we know how to match any set of characters using vague matchers, and we have the ability to repeat the patterns for any kind of sequence using multipliers, which gives you a pretty good base for matching just about anything. However, even with all this in place, there is one situation that has a tendency to come up and can be an issue. It occurs when dealing with two different and completely separate acceptable forms of input.

Let's say we are parsing some kind of form data, and for each question, we want to extract either a yes or no to be stored somewhere. With our current level of expertise, we can create a pattern similar to /[yn][eo]s?/g, which would match both yes and no. The real problem with this is that it will also match all the other six configurations of these letters, which our app probably won't know how to handle:

Matching alternated options

Luckily, Regex has a completely different system in place to hand situations like this and it is in the form...

Defining vague matchers in Regex


In this topic, we will cover character classes that tell the Regex to match a single vague character. Among the vague matches, there can be a character, digit, or an alphanumeric character.

Matching a wild card character

Let's say we wanted to find a sequence where we have 1, and then any other character followed by 3, so that it would include 123, 1b3, 1 3, 133, and so on. For these types of situations, we need to use a vague matcher in our patterns.

In the preceding example, we want to be able to use the broadest matcher possible; we can choose to put no constraints on it if we wish to and it can include any character. For these kind of situations, we have the . matcher.

A period in Regex will match any character except a new line, so it can include letters, numbers, symbols, and so on. To test this out, let's implement the aforementioned example in our HTML utility. In the text field, let's enter a few combinations to test the pattern against 123 1b3 1 3 133...

Defining ranges in Regex


Ranges in Regex allow you to create your own custom constraints, much like the ones we just went through. In a range, you can specify exactly the characters that can be used or if it's faster, you can specify the inverse, that is, the characters that do not match.

For the sake of illustration, let's say we wanted to match only abc. In this case, we could create a range similar to [abc] and it will match a single character, which is either a, b, or c. Let's test it out with the bicycle text and the /[abc]/g pattern:

Defining a range

Now, this will work, however, if you have a lot of characters you need to match, your range will become long quickly. Luckily, Regex allows you to use the (-) dash character to specify a set of characters without needing to list them out. For example, let's say we want to check whether a three lettered name is formatted correctly, and we want the first letter to be a capital letter, followed by two lower case letters. Instead of specifying...

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Description

This book is ideal for JavaScript developers and programmers who work with any type of user entry data and want sharpen their skills to become experts.

Who is this book for?

This book is ideal for JavaScript developers and programmers who work with any type of user entry data and want sharpen their skills to become experts.
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Table of Contents

7 Chapters
1. Getting Started with Regex Chevron down icon Chevron up icon
2. The Basics Chevron down icon Chevron up icon
3. Special Characters Chevron down icon Chevron up icon
4. Regex in Practice Chevron down icon Chevron up icon
5. Node.js and Regex Chevron down icon Chevron up icon
A. JavaScript Regex Cheat Sheet Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

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Full star icon Full star icon Full star icon Full star icon Empty star icon 4
(7 Ratings)
5 star 28.6%
4 star 57.1%
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2 star 14.3%
1 star 0%
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AEvangelista Dec 23, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This is written in a clear and concise manner-even a newbie, with only a basic knowledge of the JavaScript language, can easily use it. Each section builds on the previous sections. I think the book is well worth while for any JavaScript programmer.
Amazon Verified review Amazon
MiLi Dec 02, 2015
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I got a lot of Regex knowledge from this book
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poplinr Apr 20, 2016
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This is a great book on quickly getting started with writing quality regular expressions in JavaScript. More importantly, it helps you to understand the syntax and pattern development of regular expressions.
Amazon Verified review Amazon
T.M. Jul 28, 2015
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This workbook describes how to use javascript regular expressions in your code.There are several case studies for parsing and validating web forms, and a full example of analysing an apache log file using node.js. The appendix acts as a reference and covers the standard in seven tables.However, it does not cover some advenced topics like handling character encoding by using special libraries (http://xregexp.com/), or unit testing the regular expressions (like unitjs.com).
Amazon Verified review Amazon
Juri Aug 25, 2015
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IMHO, every developer should learn and know about regular expressions. While they might seem hard for some to grasp initally, the gained benefit can be huge. Whether it's to simplify your code (especially when it comes to text parsing) or simply to do some advanced search&replace within your favorite text editor (i.e. Sublime, Atom etc....). If you don't know regex yet, you have not the minimal idea of how much they can make you more productive in such situations.JavaScript Regular Expressions approaches the field of regular expressions from the JavaScript side. The book starts out slowly, giving the reader a short, but concise intro to the regular expression syntax before then diving into practical examples - which is my favorite part. The strong relation to practical scenarios is what makes the book interesting and not just purely theoretical (which is a big risk when talking about regex in general).So as mentioned, you won't regret getting this book, especially if you want to become a seasoned JavaScript developer :)
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