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Add Array.at(index) to lualib #1484

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Merged
Perryvw merged 1 commit into from
Sep 12, 2023
Merged

Add Array.at(index) to lualib #1484

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1 change: 1 addition & 0 deletions src/LuaLib.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import { LuaTarget } from "./CompilerOptions";
import { getOrUpdate } from "./utils";

export enum LuaLibFeature {
ArrayAt = "ArrayAt",
ArrayConcat = "ArrayConcat",
ArrayEntries = "ArrayEntries",
ArrayEvery = "ArrayEvery",
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13 changes: 13 additions & 0 deletions src/lualib/ArrayAt.ts
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@@ -0,0 +1,13 @@
// https://tc39.es/ecma262/multipage/indexed-collections.html#sec-array.prototype.at
// Technically the specs also allow non-numeric types to be passed as index.
// However, TypeScript types the `Array.at` index param as number so we also expect only numbers
// This behaviour also matches the implementation of other Array functions in lualib.
export function __TS__ArrayAt<T>(this: T[], relativeIndex: number): T | undefined {
const absoluteIndex = relativeIndex < 0 ? this.length + relativeIndex : relativeIndex;

if (absoluteIndex >= 0 && absoluteIndex < this.length) {
return this[absoluteIndex];
}

return undefined;
}
2 changes: 2 additions & 0 deletions src/transformation/builtins/array.ts
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Expand Up @@ -88,6 +88,8 @@ export function transformArrayPrototypeCall(

const expressionName = calledMethod.name.text;
switch (expressionName) {
case "at":
return transformLuaLibFunction(context, LuaLibFeature.ArrayAt, node, caller, ...params);
case "concat":
return transformLuaLibFunction(context, LuaLibFeature.ArrayConcat, node, caller, ...params);
case "entries":
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30 changes: 30 additions & 0 deletions test/unit/builtins/array.spec.ts
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Expand Up @@ -272,6 +272,36 @@ test("tuple.forEach", () => {
`.expectToMatchJsResult();
});

describe("at", () => {
test("valid index", () => {
util.testFunction`
const array = [1, 2, 3, 4];
return array.at(2);
`.expectToMatchJsResult();
});

test("invalid index", () => {
util.testFunction`
const array = [1, 2, 3, 4];
return array.at(10);
`.expectToMatchJsResult();
});

test("valid negative index", () => {
util.testFunction`
const array = [1, 2, 3, 4];
return array.at(-2);
`.expectToMatchJsResult();
});

test("invalid negative index", () => {
util.testFunction`
const array = [1, 2, 3, 4];
return array.at(-10);
`.expectToMatchJsResult();
});
});

test("array.forEach (%p)", () => {
util.testFunction`
const array = [0, 1, 2, 3];
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