function encodeURIComponentFast()

in src/uri.ts [477:536]
43 lines of code
22 McCabe index (conditional complexity)

function encodeURIComponentFast(uriComponent: string, allowSlash: boolean): string {
	let res: string | undefined = undefined;
	let nativeEncodePos = -1;

	for (let pos = 0; pos < uriComponent.length; pos++) {
		const code = uriComponent.charCodeAt(pos);

		// unreserved characters: https://tools.ietf.org/html/rfc3986#section-2.3
		if (
			(code >= CharCode.a && code <= CharCode.z)
			|| (code >= CharCode.A && code <= CharCode.Z)
			|| (code >= CharCode.Digit0 && code <= CharCode.Digit9)
			|| code === CharCode.Dash
			|| code === CharCode.Period
			|| code === CharCode.Underline
			|| code === CharCode.Tilde
			|| (allowSlash && code === CharCode.Slash)
		) {
			// check if we are delaying native encode
			if (nativeEncodePos !== -1) {
				res += encodeURIComponent(uriComponent.substring(nativeEncodePos, pos));
				nativeEncodePos = -1;
			}
			// check if we write into a new string (by default we try to return the param)
			if (res !== undefined) {
				res += uriComponent.charAt(pos);
			}

		} else {
			// encoding needed, we need to allocate a new string
			if (res === undefined) {
				res = uriComponent.substr(0, pos);
			}

			// check with default table first
			const escaped = encodeTable[code];
			if (escaped !== undefined) {

				// check if we are delaying native encode
				if (nativeEncodePos !== -1) {
					res += encodeURIComponent(uriComponent.substring(nativeEncodePos, pos));
					nativeEncodePos = -1;
				}

				// append escaped variant to result
				res += escaped;

			} else if (nativeEncodePos === -1) {
				// use native encode only when needed
				nativeEncodePos = pos;
			}
		}
	}

	if (nativeEncodePos !== -1) {
		res += encodeURIComponent(uriComponent.substring(nativeEncodePos));
	}

	return res !== undefined ? res : uriComponent;
}