Function decodedSourcemap

src/utils/decodedSourcemap.ts:62–106

(map: Input)

export function decodedSourcemap(map: Exclude<Input, null | undefined>): ExistingDecodedSourceMap;
export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null;
export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
	if (!map) return null;

	if (typeof map === 'string') {
		map = JSON.parse(map) as ExistingRawSourceMap;
	}
	if (!map.mappings) {
		return {
			mappings: [],
			names: [],
			sources: [],
			version: 3
		};
	}

	const originalMappings = map.mappings;
	const isAlreadyDecoded = Array.isArray(originalMappings);
	const cache: CachedSourcemapData = {
		decodedMappings: isAlreadyDecoded ? originalMappings : undefined,
		encodedMappings: isAlreadyDecoded ? undefined : originalMappings
	};

	const decodedMap = {
		...(map as ExistingRawSourceMap | ExistingDecodedSourceMap),
		// By moving mappings behind an accessor, we can avoid unneeded computation for cases
		// where the mappings field is never actually accessed. This appears to greatly reduce
		// the overhead of sourcemap decoding in terms of both compute time and memory usage.
		get mappings() {
			if (cache.decodedMappings) {
				return cache.decodedMappings;
			}
			// If decodedMappings doesn't exist then encodedMappings should.
			// The only scenario where cache.encodedMappings should be undefined is if the map
			// this was constructed from was already decoded, or if mappings was set to a new
			// decoded string. In either case, this line shouldn't get hit.
			cache.decodedMappings = cache.encodedMappings ? decode(cache.encodedMappings) : [];
			cache.encodedMappings = undefined;
			return cache.decodedMappings;
		}
	};

	sourceMapCache.set(decodedMap, cache);

	return decodedMap;
}