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Regular Expressions Test Method

Regular expressions are used in programming languages to match parts of strings. You create patterns to help you do that matching.

If you want to find the word the in the string The dog chased the cat, you could use the following regular expression: /the/. Notice that quote marks are not required within the regular expression.

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.

let testStr = "freeCodeCamp";
let testRegex = /Code/;
testRegex.test(testStr);

The test method here returns true.

In the last challenge, you searched for the word Hello using the regular expression /Hello/. That regex searched for a literal match of the string Hello. Here’s another example searching for a literal match of the string Kevin:

let testStr = "Hello, my name is Kevin.";
let testRegex = /Kevin/;
testRegex.test(testStr);

This test call will return true.

Any other forms of Kevin will not match. For example, the regex /Kevin/ will not match kevin or KEVIN.

let wrongRegex = /kevin/;
wrongRegex.test(testStr);

This test call will return false.

A future challenge will show how to match those other forms as well.

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Matt is the author of five Apress books including Learn RStudio IDE, Quick, Effective, and Productive Data Science, Objective-C Recipes, Swift Quick Syntax Reference, Objective-C Quick Reference, and the upcoming Pro Data Visualization with R and JavaScript. He has over 20 years of experience in technology, psychometrics, and data analytics working in major higher education institutions such as The College Board and Educational Testing Service. He has earned a Master’s degree in Information Systems Management and a Bachelor’s degree in Quantitative Psychology.