(third) Add typings for Intl.ListFormat

Author: stasm

experiments/stasm/third/example/example_list.ts

@@ -22,22 +22,20 @@ class Person {
 
 // TODO(stasm): This is generic enough that it could be in impl/runtime.ts.
 class ListValue<T> extends RuntimeValue<Array<T>> {
-	private opts: Record<string, string>; // ListFormatOptions
+	private opts: Intl.ListFormatOptions;
 
-	constructor(value: Array<T>, opts: Record<string, string> = {}) {
+	constructor(value: Array<T>, opts: Intl.ListFormatOptions = {}) {
 		super(value);
 		this.opts = opts;
 	}
 
 	formatToString(ctx: FormattingContext): string {
 		// TODO(stasm): Cache ListFormat.
-		// @ts-ignore
 		let lf = new Intl.ListFormat(ctx.locale, this.opts);
 		return lf.format(this.value);
 	}
 
 	*formatToParts(ctx: FormattingContext): IterableIterator<FormattedPart> {
-		// @ts-ignore
 		let lf = new Intl.ListFormat(ctx.locale, this.opts);
 		yield* lf.formatToParts(this.value);
 	}

experiments/stasm/third/impl/intl.d.ts

@@ -0,0 +1,25 @@
+declare namespace Intl {
+	interface ListFormatOptions {
+		// I added `string` to avoid having to validate the exact values of options.
+		localeMatcher?: string | "best fit" | "lookup";
+		type?: string | "conjunction" | "disjunction | unit";
+		style?: string | "long" | "short" | "narrow";
+	}
+
+	type ListFormatPartTypes = "literal" | "element";
+
+	interface ListFormatPart {
+		type: ListFormatPartTypes;
+		value: string;
+	}
+
+	interface ListFormat {
+		format(value?: Array<unknown>): string;
+		formatToParts(value?: Array<unknown>): ListFormatPart[];
+	}
+
+	var ListFormat: {
+		new (locales?: string | string[], options?: ListFormatOptions): ListFormat;
+		(locales?: string | string[], options?: ListFormatOptions): ListFormat;
+	};
+}