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feat(importStar): Cache non‑module results #80

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feat(importStar): Cache non‑module results #80

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21 changes: 14 additions & 7 deletions tslib.es6.js
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Original file line number Diff line number Diff line change
Expand Up @@ -209,13 +209,20 @@ var __setModuleDefault = Object.create ? (function(o, v) {
o["default"] = v;
};

export function __importStar(mod) {
if (mod && mod.__esModule) return mod;
var result = {};
if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
return result;
}
export var __importStar = function (mod) {
var cache = typeof WeakMap === "function" ? new WeakMap() : null;
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Are you proposing this be implemented in TypeScript as well for inline helper emit? If so we'd need to introduce a checker error if you declare your own value named WeakMap at the top of a module.

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The issue there is that this is supposed to be an optimisation when two different modules that use tslib import the same CommonJS module, the value returned by __importStar is the same value for both imports, e.g.:

// modA.js
Object.defineProperty(exports, "__esModule", { value: true });
var tslib = require("tslib");

exports.example = tslib.__importStar(require("example"));
// modB.js
Object.defineProperty(exports, "__esModule", { value: true });
var tslib = require("tslib");

exports.example = tslib.__importStar(require("example"));
// test.js
var assert = require("assert");

var modA = require("./modA.js");
var modB = require("./modA.js");

// The following passes regardless of whether `example` has `__esModule` or not:
assert.strictEqual(modA.example, modB.example);

It doesn’t make sense to include the module cache in inline helpers, as modA and modB would then each have their own cache, and every new local __imporStar call would then have a cache miss, since the cache wouldn’t be global.

__importStar = function (mod) {
if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { default: mod };
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nit: Parens aren't needed here, since && has higher precedence than ||.

Suggested change
if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { default: mod };
if (mod === null || typeof mod !== "object" && typeof mod !== "function") return { default: mod };

if (mod.__esModule) return mod;
if (cache && cache.has(mod)) return cache.get(mod);
var result = {};
for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
if (cache) cache.set(mod, result);
return result;
}
return __importStar(mod);
};

export function __importDefault(mod) {
return (mod && mod.__esModule) ? mod : { default: mod };
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17 changes: 12 additions & 5 deletions tslib.js
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Original file line number Diff line number Diff line change
Expand Up @@ -251,11 +251,18 @@ var __createBinding;
};

__importStar = function (mod) {
if (mod && mod.__esModule) return mod;
var result = {};
if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
return result;
var cache = typeof WeakMap === "function" ? new WeakMap() : null;
__importStar = function (mod) {
if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { default: mod };
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nit: Parens aren't necessary here.

Suggested change
if (mod === null || (typeof mod !== "object" && typeof mod !== "function")) return { default: mod };
if (mod === null || typeof mod !== "object" && typeof mod !== "function") return { default: mod };

if (mod.__esModule) return mod;
if (cache && cache.has(mod)) return cache.get(mod);
var result = {};
for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
if (cache) cache.set(mod, result);
return result;
}
return __importStar(mod);
};

__importDefault = function (mod) {
Expand Down