esbuild 0.17.4

v0.17.4

on Node.js NPM

Implement HTTP HEAD requests in serve mode (#2851)

Previously esbuild's serve mode only responded to HTTP GET requests. With this release, esbuild's serve mode will also respond to HTTP HEAD requests, which are just like HTTP GET requests except that the body of the response is omitted.

Permit top-level await in dead code branches (#2853)

Adding top-level await to a file has a few consequences with esbuild:

1. It causes esbuild to assume that the input module format is ESM, since top-level await is only syntactically valid in ESM. That prevents you from using module and exports for exports and also enables strict mode, which disables certain syntax and changes how function hoisting works (among other things).
2. This will cause esbuild to fail the build if either top-level await isn't supported by your language target (e.g. it's not supported in ES2021) or if top-level await isn't supported by the chosen output format (e.g. it's not supported with CommonJS).
3. Doing this will prevent you from using require() on this file or on any file that imports this file (even indirectly), since the require() function doesn't return a promise and so can't represent top-level await.

This release relaxes these rules slightly: rules 2 and 3 will now no longer apply when esbuild has identified the code branch as dead code, such as when it's behind an if (false) check. This should make it possible to use esbuild to convert code into different output formats that only uses top-level await conditionally. This release does not relax rule 1. Top-level await will still cause esbuild to unconditionally consider the input module format to be ESM, even when the top-level await is in a dead code branch. This is necessary because whether the input format is ESM or not affects the whole file, not just the dead code branch.

Fix entry points where the entire file name is the extension (#2861)

Previously if you passed esbuild an entry point where the file extension is the entire file name, esbuild would use the parent directory name to derive the name of the output file. For example, if you passed esbuild a file ./src/.ts then the output name would be src.js. This bug happened because esbuild first strips the file extension to get ./src/ and then joins the path with the working directory to get the absolute path (e.g. join("/working/dir", "./src/") gives /working/dir/src). However, the join operation also canonicalizes the path which strips the trailing /. Later esbuild uses the "base name" operation to extract the name of the output file. Since there is no trailing /, esbuild returns "src" as the base name instead of "", which causes esbuild to incorrectly include the directory name in the output file name. This release fixes this bug by deferring the stripping of the file extension until after all path manipulations have been completed. So now the file ./src/.ts will generate an output file named .js.

Support replacing property access expressions with inject

At a high level, this change means the inject feature can now replace all of the same kinds of names as the define feature. So inject is basically now a more powerful version of define, instead of previously only being able to do some of the things that define could do.

Soem background is necessary to understand this change if you aren't already familiar with the inject feature. The inject feature lets you replace references to global variable with a shim. It works like this:

1. Put the shim in its own file
2. Export the shim as the name of the global variable you intend to replace
3. Pass the file to esbuild using the inject feature

For example, if you inject the following file using --inject:./injected.js:

// injected.js
let processShim = { cwd: () => '/' }
export { processShim as process }

Then esbuild will replace all references to process with the processShim variable, which will cause process.cwd() to return '/'. This feature is sort of abusing the ESM export alias syntax to specify the mapping of global variables to shims. But esbuild works this way because using this syntax for that purpose is convenient and terse.

However, if you wanted to replace a property access expression, the process was more complicated and not as nice. You would have to:

1. Put the shim in its own file
2. Export the shim as some random name
3. Pass the file to esbuild using the inject feature
4. Use esbuild's define feature to map the property access expression to the random name you made in step 2

For example, if you inject the following file using --inject:./injected2.js --define:process.cwd=someRandomName:

// injected2.js
let cwdShim = () => '/'
export { cwdShim as someRandomName }

Then esbuild will replace all references to process.cwd with the cwdShim variable, which will also cause process.cwd() to return '/' (but which this time will not mess with other references to process, which might be desirable).

With this release, using the inject feature to replace a property access expression is now as simple as using it to replace an identifier. You can now use JavaScript's "arbitrary module namespace identifier names" feature to specify the property access expression directly using a string literal. For example, if you inject the following file using --inject:./injected3.js:

// injected3.js
let cwdShim = () => '/'
export { cwdShim as 'process.cwd' }

Then esbuild will now replace all references to process.cwd with the cwdShim variable, which will also cause process.cwd() to return '/' (but which will also not mess with other references to process).

In addition to inserting a shim for a global variable that doesn't exist, another use case is replacing references to static methods on global objects with cached versions to both minify them better and to make access to them potentially faster. For example:

// Injected file
let cachedMin = Math.min
let cachedMax = Math.max
export {
  cachedMin as 'Math.min',
  cachedMax as 'Math.max',
}

// Original input
function clampRGB(r, g, b) {
  return {
    r: Math.max(0, Math.min(1, r)),
    g: Math.max(0, Math.min(1, g)),
    b: Math.max(0, Math.min(1, b)),
  }
}

// Old output (with --minify)
function clampRGB(a,t,m){return{r:Math.max(0,Math.min(1,a)),g:Math.max(0,Math.min(1,t)),b:Math.max(0,Math.min(1,m))}}

// New output (with --minify)
var a=Math.min,t=Math.max;function clampRGB(h,M,m){return{r:t(0,a(1,h)),g:t(0,a(1,M)),b:t(0,a(1,m))}}