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Cannot read properties of undefined (reading 'includes') in Sanity schema

1 replies
Last updated: Nov 29, 2025
Need help with an error, it was working well before and now it isn't. I am not sure why.
Error: Cannot read properties of undefined (reading 'includes')
TypeError: Cannot read properties of undefined (reading 'includes')

I think it might be from these lines of code:
{
name: 'projectType',
title: 'Type',
type: 'array',
of: [{type: 'string'}],
options: {
list: [
{title: 'Building', value: 'building'},
{title: 'Districts', value: 'districts'},
],
layout: 'radio',
},
description:
'These are the types of properties in a project. Building will have number of floors and units. Districts will have number of villas/townhouses.',
},
{
name: 'numFloors',
title: 'Number of Floors',
type: 'number',
hidden: ({parent}: {parent: {projectType: string[]}}) =>
!parent.projectType.includes('building'),
description: 'It indicates the number of floors in the building.',
},
{
name: 'numUnits',
title: 'Number of Units',
type: 'number',
hidden: ({parent}: {parent: {projectType: string[]}}) =>
!parent.projectType.includes('building'),
description: 'It indicates the number of units in the building.',
},
{
name: 'numOfHouses',
title: 'Number of Villas/Townhouses',
type: 'number',
hidden: ({parent}: {parent: {projectType: string[]}}) =>
!parent.projectType.includes('districts'),
description: 'It indicates the number of villas or townhouses in the district.',
},
AI Update

The error is happening because parent.projectType is undefined when your conditional hidden functions run, but you're calling .includes() on it without checking if it exists first.

Fix: Add optional chaining to safely handle undefined values:

hidden: ({parent}: {parent: {projectType?: string[]}}) =>
  !parent.projectType?.includes('building'),

Apply this pattern to all three conditional fields (numFloors, numUnits, and numOfHouses).

The ?. operator will return undefined if projectType is undefined, and since !undefined is true, the fields will be hidden by default when no project type is selected - which is exactly what you want.

This typically breaks when creating new documents or when the projectType field hasn't been set yet. The optional chaining prevents the error and provides sensible default behavior.

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