NativeScript/packages/core/ui/frame/frame-stack.ts

// Types.
import { FrameBase } from './frame-common';

export const frameStack: Array<FrameBase> = [];

export function topmost(): FrameBase {
	if (frameStack.length > 0) {
		return frameStack[frameStack.length - 1];
	}

	return undefined;
}

export function _pushInFrameStack(frame: FrameBase): void {
	if (frame._isInFrameStack && frameStack[frameStack.length - 1] === frame) {
		return;
	}

	if (frame._isInFrameStack) {
		const indexOfFrame = frameStack.indexOf(frame);
		frameStack.splice(indexOfFrame, 1);
	}

	frameStack.push(frame);
	frame._isInFrameStack = true;
}

export function _popFromFrameStack(frame: FrameBase): void {
	if (!frame._isInFrameStack) {
		return;
	}

	const top = topmost();
	if (top !== frame) {
		throw new Error('Cannot pop a Frame which is not at the top of the navigation stack.');
	}

	frameStack.pop();
	frame._isInFrameStack = false;
}

export function _removeFromFrameStack(frame: FrameBase): void {
	if (!frame._isInFrameStack) {
		return;
	}

	const index = frameStack.indexOf(frame);
	frameStack.splice(index, 1);
	frame._isInFrameStack = false;
}