Guide: Sift through Text with Regular Expressions

Guide
1

Regular expressions are used to find certain words or patterns inside of strings.

Regular expressions are usually surrounded by / symbols.

For example, if we wanted to find the number of times the word the occurred in the string The dog chased the cat, we could use the following regular expression: /the+/gi

Let’s break this down a bit:

the is the pattern we want to match.

  • + means we want to find one or more occurrences of this pattern.
  • g means that we want to search the entire string for this pattern.
  • i means that we want to ignore the case (uppercase or lowercase) when searching for the pattern.
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2

Hi.
Quick (hopefully) question.
In this challenge/lesson console show the number of found references from this and only this line:
var andCount = testString.match(expression).length;
It is happening “behind the scene” someway or am I missing something ?

Console stopped to update the number even when I just change variable (andCount) name.

3

What’s the purpose of attaching the length property to the match() function? Wouldn’t the match function search the entire string regardless of using the length property?

4

That’s the same question I asked. If you remove the length property it turns out you get an array:

var andCount = testString.match(expression); --> output [“and”, “and”]

So the length property is just counting the terms in the array i.e. 2

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5

All the challenge required was to test your understanding of regular expression,like this:

var expression = /and/gi;

// Setup
var testString = “Ada Lovelace and Charles Babbage designed the first computer and the software that would have run on it.”;

// Example
var expressionToGetSoftware = /software/gi;
var softwareCount = testString.match(expressionToGetSoftware).length;

// Only change code below this line.

var expression = /and/gi; // Changed Line

// Only change code above this line

// This code counts the matches of expression in testString
var andCount = testString.match(expression).length;

1 Like
6

My answer:

/ / Only change code below this line.

var expression = /and/gi;  // Change this Line
var expressionToGetAnd = testString.match(expression).length;
// Only change code above this line

// This code counts the matches of expression in testString
var andCount = testString.match(expression).length;
1 Like