How Devtools Map Minified Js Code Back to Your Typescript Source Code

Posted2 months agoActive2 months ago

manojvivek

107 points

16 comments

polarsignals.comTechstory

calmpositive

Debate

20/100

Source MapsJavascriptTypescriptDebugging

Key topics

Source Maps

Javascript

Typescript

Debugging

The article explains how source maps work to map minified JS code back to TypeScript source code, sparking discussion on related tools and security implications.

Snapshot generated from the HN discussion

Discussion Activity

Moderate engagement

First comment

16m

Peak period

0-6h

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Comment distribution16 data points

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01Story posted
Nov 4, 2025 at 10:21 AM EST
2 months ago
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Nov 6, 2025 at 4:45 PM EST
2 months ago
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Discussion (16 comments)

Showing 16 comments

tantalor

2 months ago

5 replies

> Notice how the decoded values give relative positions, each value represents the difference from the previous position, not absolute coordinates. This is crucial: instead of encoding large column numbers like 27698 in minified files, source maps only store small deltas like +7 or +15, making the encoded strings much more compact.

Wouldn't "offset" be a more apt term?

manojvivekAuthor

2 months ago

1 reply

To me, “offset” sounds more like the distance from the start, whereas here the values are relative to the previous segment. Not a native english speaker, so I could be wrong.

tantalor

2 months ago

1 reply

Offset is difference from a starting point or a previous position

jagged-chisel

2 months ago

1 reply

“Offset” is not enough on its own. Offset from what? Start of file? Absolute offset. Previous offset? Relative offset.

willrshansen

2 months ago

1 reply

2nd order offset. The offset from the <offset from the start of the file>

eat_veggies

2 months ago

1 reply

perhaps the delta between offsets

jagged-chisel

2 months ago

We’re gonna need the delta of deltas

hanikesn

2 months ago

1 reply

Delta Encoding is the common term

tracker1

2 months ago

Agreed... Delta Encoding, or even Delta Offset would work together.

paulddraper

2 months ago

1 reply

Delta and offset mean the same thing — the difference between two amounts.

Delta is perhaps slightly more obscure outside of a math setting. Perhaps.

saghm

2 months ago

I feel like choosing the synonym that happens to be one letter shorter when the operation is literally intended to track things in a way that's more conscise is about as "apt" as it could be!

accrual

2 months ago

In this case I feel it's like six of one and a half-dozen of the other.

Delta definition 4: (mathematics, physics, engineering) The symbol Δ; A change in a quantity, likely from "d" for "difference"

Offset definition 7: The distance by which one thing is out of alignment with another.

Got these from Wiktionary:

* https://en.wiktionary.org/wiki/delta

* https://en.wiktionary.org/wiki/offset

recursive

2 months ago

It sounds equally apt to my ear. I've used both words for this concept in the past.

kayson

2 months ago

I love it when things are displayed so nicely on mobile. This could've been a pain to read and get through but it was actually quite pleasant.

zb3

2 months ago

Tangentially related, but last year I've made a tool to recover original sources from web apps which expose source maps (with the sourcesContent value present), including enumerating all lazily loaded chunks:

https://github.com/zb3/getfrontend

pseufaux

2 months ago

Recent related post where Apple seemingly forgot to disable source maps for the App Store

Apple's App Store Full Front End Source Code

https://news.ycombinator.com/item?id=45804664

edit: formatting

View full discussion on Hacker News

ID: 45812000Type: storyLast synced: 11/20/2025, 7:55:16 PM

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