I am working on next.js 15 project using typescript. The goal is to create nested Navigation. When I run npm run dev it compiles correctly but when I try to build the project I am getting the following error:

Type error: Type 'menuListProps | undefined' is not assignable to type 'menuItemProps[]'.                                               
  Type 'undefined' is not assignable to type 'menuItemProps[]'.

  90 |                                  <li key={id}>                                                                                   
  91 |                                          <h2>{title}</h2>                                                                        
> 92 |                                          <MenuContent subMenuItems={subMenuItems} />                                             
     |                                                       ^                                                                          
  93 |                                  </li>                                                                                           
  94 |                          </>                                                                                                     
  95 |                  )  

data for menu:

const menuItems = [

    {
        id:getRandomInt(maxIntegerRandom),
        title:"a",
        subMenuItems: [
        {
            id:getRandomInt(maxIntegerRandom),
            title:"a1",
            subMenuItems: [
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a11",
            },
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a12",

            },
            ],
        },
        {
            id:getRandomInt(maxIntegerRandom),
            title:"a2",
            subMenuItems: [
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a21",
            },
            ],
        },  
        ]

    }
]

types definitions:

type menuListProps = {
    passedMenuItems: menuItemProps[];
}

type menuItemProps = {
    id: number;
    title: string;

    shortTitle?: string;
    description?: string;
    shortDescription?: string;
    path?: string;
    image?: string;
    icon?: string;

    hideForHamburgerMenu?: boolean;

    subMenuItems?: menuListProps;
}

components:

function MenuContent(props: menuListProps){

    const { passedMenuItems } = props;

    let toRender = null;

    toRender = passedMenuItems.map( (menuItem) => MenuItem(menuItem) )

    return (
        <>
            <ul>
                {toRender}
            </ul>
        </>
    )
}

function MenuItem (props: menuItemProps){
    const { id, path, title, subMenuItems, hideForHamburgerMenu } = props;

    if (!("hideForHamburgerMenu" in props && hideForHamburgerMenu))
    {
        if ("subMenuItems" in props)
            return (
                <>
                    <li key={id}>
                        <h2>{title}</h2>
                        <MenuContent passedMenuItems={subMenuItems} />
                    </li>
                </>
            )

        else 
            return (

                <li key={id}>
                    <h2>{title}</h2>
                </li>
            )
    }
}

default function:

export default function MobileAsideMainMenu(){
    return(
        <>
            <MenuContent passedMenuItems={menuItems} />
        </>
    )
}

Please help me investigate what am I doing wrong?

I am working on next.js 15 project using typescript. The goal is to create nested Navigation. When I run npm run dev it compiles correctly but when I try to build the project I am getting the following error:

Type error: Type 'menuListProps | undefined' is not assignable to type 'menuItemProps[]'.                                               
  Type 'undefined' is not assignable to type 'menuItemProps[]'.

  90 |                                  <li key={id}>                                                                                   
  91 |                                          <h2>{title}</h2>                                                                        
> 92 |                                          <MenuContent subMenuItems={subMenuItems} />                                             
     |                                                       ^                                                                          
  93 |                                  </li>                                                                                           
  94 |                          </>                                                                                                     
  95 |                  )  

data for menu:

const menuItems = [

    {
        id:getRandomInt(maxIntegerRandom),
        title:"a",
        subMenuItems: [
        {
            id:getRandomInt(maxIntegerRandom),
            title:"a1",
            subMenuItems: [
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a11",
            },
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a12",

            },
            ],
        },
        {
            id:getRandomInt(maxIntegerRandom),
            title:"a2",
            subMenuItems: [
            {
                id:getRandomInt(maxIntegerRandom),
                title:"a21",
            },
            ],
        },  
        ]

    }
]

types definitions:

type menuListProps = {
    passedMenuItems: menuItemProps[];
}

type menuItemProps = {
    id: number;
    title: string;

    shortTitle?: string;
    description?: string;
    shortDescription?: string;
    path?: string;
    image?: string;
    icon?: string;

    hideForHamburgerMenu?: boolean;

    subMenuItems?: menuListProps;
}

components:

function MenuContent(props: menuListProps){

    const { passedMenuItems } = props;

    let toRender = null;

    toRender = passedMenuItems.map( (menuItem) => MenuItem(menuItem) )

    return (
        <>
            <ul>
                {toRender}
            </ul>
        </>
    )
}

function MenuItem (props: menuItemProps){
    const { id, path, title, subMenuItems, hideForHamburgerMenu } = props;

    if (!("hideForHamburgerMenu" in props && hideForHamburgerMenu))
    {
        if ("subMenuItems" in props)
            return (
                <>
                    <li key={id}>
                        <h2>{title}</h2>
                        <MenuContent passedMenuItems={subMenuItems} />
                    </li>
                </>
            )

        else 
            return (

                <li key={id}>
                    <h2>{title}</h2>
                </li>
            )
    }
}

default function:

export default function MobileAsideMainMenu(){
    return(
        <>
            <MenuContent passedMenuItems={menuItems} />
        </>
    )
}

Please help me investigate what am I doing wrong?

• javascript
• typescript

• Type definition is subMenuItems?: menuListProps but your data is an array. You could change it to subMenuItems?: MenuItem[]. – keithwalsh Commented Nov 15, 2024 at 23:16

1 Answer 1

Your type menuItemProps defines the property as subMenuItems?: menuListProps which means two things:

1. The property is optional, it does not need to be specified when creating an instance;
2. The actual type of the property becomes undefined | menuListProps.

Also I see some confusion between types, as if you are showing us bits of code that do not belong together or that have been edited in between. Sometimes an object itself seems to be an array, other times that same(?) object has a property that contains an array.

Anyway, when you use this prop in <MenuContent subMenuItems={subMenuItems} />, it is not compatible with the menuListProps that it expects.

You have an “if" to "guard the usage", but that is not a kind of type guard or type narrowing that Typescript can recognize.

If you change it to this:

if (subMenuItems !== undefined)

then I expect at least the mentioned error to go away, because now Typescript knows that inside the "if" the variable can not be undefined.

However there is more to be done, but until you provide consistent code, I can not comment on what you should actually use everywhere.