Bundling no longer unnecessarily transforms class syntax (#1360, #1328, #1524, #2416)
When bundling, esbuild automatically converts top-level class statements to class expressions. Previously this conversion had the unfortunate side-effect of also transforming certain other class-related syntax features to avoid correctness issues when the references to the class name within the class body. This conversion has been reworked to avoid doing this:
// Original code
export class Foo {
static foo = () => Foo
}
// Old output (with --bundle)
var _Foo = class {
};
var Foo = _Foo;
__publicField(Foo, "foo", () => _Foo);
// New output (with --bundle)
var Foo = class _Foo {
static foo = () => _Foo;
};
This conversion process is very complicated and has many edge cases (including interactions with static fields, static blocks, private class properties, and TypeScript experimental decorators). It should already be pretty robust but a change like this may introduce new unintentional behavior. Please report any issues with this upgrade on the esbuild bug tracker.
You may be wondering why esbuild needs to do this at all. One reason to do this is that esbuild's bundler sometimes needs to lazily-evaluate a module. For example, a module may end up being both the target of a dynamic import() call and a static import statement. Lazy module evaluation is done by wrapping the top-level module code in a closure. To avoid a performance hit for static import statements, esbuild stores top-level exported symbols outside of the closure and references them directly instead of indirectly.
Another reason to do this is that multiple JavaScript VMs have had and continue to have performance issues with TDZ (i.e. "temporal dead zone") checks. These checks validate that a let, or const, or class symbol isn't used before it's initialized. Here are two issues with well-known VMs:
JavaScriptCore had a severe performance issue as their TDZ implementation had time complexity that was quadratic in the number of variables needing TDZ checks in the same scope (with the top-level scope typically being the worst offender). V8 has ongoing issues with TDZ checks being present throughout the code their JIT generates even when they have already been checked earlier in the same function or when the function in question has already been run (so the checks have already happened).
Due to esbuild's parallel architecture, esbuild both a) needs to convert class statements into class expressions during parsing and b) doesn't yet know whether this module will need to be lazily-evaluated or not in the parser. So esbuild always does this conversion during bundling in case it's needed for correctness (and also to avoid potentially catastrophic performance issues due to bundling creating a large scope with many TDZ variables).
Enforce TDZ errors in computed class property keys (#2045)
JavaScript allows class property keys to be generated at run-time using code, like this:
Previously esbuild treated references to the containing class name within computed property keys as a reference to the partially-initialized class object. That meant code that attempted to reference properties of the class object (such as the code above) would get back undefined instead of throwing an error.
This release rewrites references to the containing class name within computed property keys into code that always throws an error at run-time, which is how this JavaScript code is supposed to work. Code that does this will now also generate a warning. You should never write code like this, but it now should be more obvious when incorrect code like this is written.
This changelog documents all esbuild versions published in the year 2022 (versions 0.14.11 through 0.16.12).
0.16.12
Loader defaults to js for extensionless files (#2776)
Certain packages contain files without an extension. For example, the yargs package contains the file yargs/yargs which has no extension. Node, Webpack, and Parcel can all understand code that imports yargs/yargs because they assume that the file is JavaScript. However, esbuild was previously unable to understand this code because it relies on the file extension to tell it how to interpret the file. With this release, esbuild will now assume files without an extension are JavaScript files. This can be customized by setting the loader for "" (the empty string, representing files without an extension) to another loader. For example, if you want files without an extension to be treated as CSS instead, you can do that like this:
In addition, the "type" field in package.json files now only applies to files with an explicit .js, .jsx, .ts, or .tsx extension. Previously it was incorrectly applied by esbuild to all files that had an extension other than .mjs, .mts, .cjs, or .cts including extensionless files. So for example an extensionless file in a "type": "module" package is now treated as CommonJS instead of ESM.
0.16.11
Avoid a syntax error in the presence of direct eval (#2761)
The behavior of nested function declarations in JavaScript depends on whether the code is run in strict mode or not. It would be problematic if esbuild preserved nested function declarations in its output because then the behavior would depend on whether the output was run in strict mode or not instead of respecting the strict mode behavior of the original source code. To avoid this, esbuild transforms nested function declarations to preserve the intended behavior of the original source code regardless of whether the output is run in strict mode or not:
// Original code
if (true) {
function foo() {}
console.log(!!foo)
foo = null
console.log(!!foo)
}
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Bumps esbuild from 0.15.5 to 0.18.4.
Release notes
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... (truncated)
Changelog
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Commits
bfc5a0f
publish 0.18.4 to npm5eb8f03
fix #3169: print negative properties as computed73ee85a
overhaul esbuild's class transform (#3167)7bd06b0
fix function tree-shaking with--keep-names
b1887eb
copy setup code to new ci jobf279568
ci: try type checking tsc using esbuild-built tsc1d3c0a1
use "inner class name" instead of "shadow name"9224cce
publish 0.18.3 to npm35fd509
fix #3161: panic when minifyingstatic {}
a7a9096
publish 0.18.2 to npmDependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting
@dependabot rebase
.Dependabot commands and options
You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)