Text Processing with JavaScript

Recipe 47

Testing a Pattern with the Positive Lookahead

Task

Suppose your task is to fix a mistake in several documents that inaccurately list a company’s revenue in dollars, instead of euros. You need to find all instances of “$90.3 million” and replace “$” with “€.”

So, what you need is a regex pattern that finds “$90.3 million” in a sentence such as this:

"The Company posted a September quarter record revenue of $90.3 million,
up 8 percent year over year."

But you want to match and replace only the currency sign, not the entire string. You need a way to exclude “90.3 million” from the match result.

Solution

Use a positive lookahead denoted by (?= ... ) to match the part of the string that you don’t want to include in the result:

part_2/positive_lookahead/positive_lookahead_ex1.js ...