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RegEx
REGEX108
3
Search And Replace Safely
RegEx replacement can clean many matches, but only after the search is tested.
Why is RegEx replacement risky?
RegEx replacement is risky because one pattern can change many pieces of text at once, including text you did not mean to change.
Finding text is safer than replacing text.
A bad search shows the wrong matches.
A bad replace changes the wrong matches.
That is why replacement work should happen in steps.
Find first, inspect matches, replace second, then check the result.
Replacing repeated spaces
const messy = "Rick learns RegEx";
const cleaned = messy.replace(/[ ]+/g, " ");
console.log(cleaned);
// Rick learns RegEx
[ ]+ matches one or more spaces.
g means global, so all matches are replaced.
replace() creates cleaned text.
The replacement is one normal space.
This is safe because the pattern is narrow and easy to test.
Cleanup
Replacement can clean messy text quickly.
Speed
One replacement can update many matches.
Risk
A broad pattern can damage content.
Workflow
Search, inspect, replace, then verify.
Too broad
Narrow cleanup
text.replace(/[ ]+/g, " ")
Ask ChatGPT: "Is this replacement pattern narrow enough, and what examples should I test before running it?"
Create text with repeated spaces.
Write a pattern that finds one or more spaces.
Replace repeated spaces with one space.
Test before and after output.
Explain why find must come before replace.
Replacing before checking matches.
Using a pattern that matches too much.
Forgetting the global flag when all matches should change.
Not keeping a backup before changing files.
Testing only clean input instead of messy input.
Use RegEx replacement carefully by testing the search before changing text.
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