Question 1

How do I use jsfmt to refactor code from an old library?

Accepted Answer

Use the --rewrite flag with a pattern like '_.each(a, b) -> a.forEach(b)' to automate conversions, as shown in the rewrite examples. This applies AST-based transformations across files for large-scale updates.

Question 2

jsfmt vs Prettier: which should I choose for formatting?

Accepted Answer

jsfmt is better if you need integrated AST searching/rewriting with formatting, while Prettier excels at zero-config, opinionated formatting with wider ecosystem support. jsfmt uses esformatter under the hood, which may offer more customization but less consistency.

Question 3

Can jsfmt handle JSON files or just JavaScript?

Accepted Answer

Yes, it supports JSON formatting and validation via the --json flag and jsfmt.formatJSON API, making it useful for configuration files alongside JavaScript code.

Question 4

How to set up jsfmt with my editor like Vim?

Accepted Answer

Install plugins like vim-jsfmt.vim from the Links section; they automatically run jsfmt on save, but require global npm installation and configuration via .jsfmtrc for style rules.

Question 5

Does jsfmt work with TypeScript or JSX?

Accepted Answer

No native TypeScript support; for JSX, you must manually integrate the esformatter-jsx plugin as noted in the Plugins section, adding setup complexity.

Question 6

Is jsfmt still actively maintained?

Accepted Answer

The last changelog entry is v0.4.0 from 2014, and dependencies may be outdated, so maintenance is questionable compared to tools like Prettier with frequent updates.

Question 7

How to write a search pattern to find specific code usages?

Accepted Answer

Use the --search flag with a JavaScript expression like 'a.slice(b, c)', which outputs matches based on AST patterns, similar to rewrite rules but for identification only.

jsfmt

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