JavaScript Cookbook, 3rd Edition

Chapter 2. Strings and Regular Expressions

Here’s a trivia question for your next JavaScript party: how many data types are there in the world’s most popular language?

The answer is eight, but they might not be what you expect. JavaScript’s eight data types are:

• Number

• String

• Boolean

• BigInt (for very large integers)

• Symbol (for unique identifiers)

• Object (the root of every other JavaScript type)

• undefined (a variable that hasn’t been assigned a value)

• null (a missing object)

The recipes in this book feature all of these ingredients. In this chapter, you’ll turn your focus to the text-manipulating power of strings.

Checking for an Existing, Nonempty String

Problem

You want to verify that a variable is defined, is a string, and is not empty before you use it.

Solution

Before you start working with a string, you often need to validate that it’s safe to use. When you do, there are different questions you might ask.

If you want to make sure that your variable is a string (not just a variable that can be converted to a string), you use this test:

if (typeof unknownVariable === 'string') {
  // unknownVariable is a string
}

If you want to check that you have a nonempty string (not the zero-length string ''), you can tighten your verification like this:

if (typeof unknownVariable === 'string' && unknownVariable.length > 0) {
  // This is a genuine string with characters or whitespace in it
}

Optionally, you may want to reject strings that are made up of whitespace ...