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

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

export let 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;
}