Thanks for your reaction @JeffreyWay! Too bad my English isn't good enough to make myself clear at all times.

If I have a form to edit a user (for example). You would have to prefill all fields with data from your user object.

My guess would be to do this in the setup of the form, so:

setup() { const form = useForm({ name: this.user.name }) return {form}},

While setting up the form with name: null works fine; setting a value does not work at all.

Doing so will get me

runtime-core.esm-bundler.js?d2dd:6584 [Vue warn]: Unhandled error during execution of setup function 
  at <UsersEdit errors= Object appName="Roosteren" env="local"  ... > 
  at <ColumnLayout main-content-set= Object main-content-overflow=true > 
  at <UsersLayout errors= Object appName="Roosteren" env="local"  ... > 
  at <Layout errors= Object appName="Roosteren" env="local"  ... > 
  at <Inertia initialPage= Object initialComponent= Object resolveComponent=fn<m>  ... > 
  at <App>
warn @ runtime-core.esm-bundler.js?d2dd:6584

[Vue warn]: Unhandled error during execution of scheduler flush. This is likely a Vue internals bug. Please open an issue at https://new-issue.vuejs.org/?repo=vuejs/vue-next 
  at <UsersEdit errors= Object[[Prototype]]: Objectconstructor: ƒ Object()hasOwnProperty: ƒ hasOwnProperty()isPrototypeOf: ƒ isPrototypeOf()propertyIsEnumerable: ƒ propertyIsEnumerable()toLocaleString: ƒ toLocaleString()toString: ƒ toString()valueOf: ƒ valueOf()__defineGetter__: ƒ __defineGetter__()__defineSetter__: ƒ __defineSetter__()__lookupGetter__: ƒ __lookupGetter__()__lookupSetter__: ƒ __lookupSetter__()__proto__: (...)get __proto__: ƒ __proto__()set __proto__: ƒ __proto__() appName="Roosteren" env="local"  ... > 
  at <ColumnLayout main-content-set= Object main-content-overflow=true > 
  at <UsersLayout errors= Object appName="Roosteren" env="local"  ... > 
  at <Layout errors= Object appName="Roosteren" env="local"  ... > 
  at <Inertia initialPage= Object initialComponent= Object resolveComponent=fn<m>  ... > 
  at <App>
warn @ runtime-core.esm-bundler.js?d2dd:6584

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'user')
    at setup (webpack-internal:///./node_modules/babel-loader/lib/index.js??clonedRuleSet-5.use[0]!./node_modules/vue-loader/dist/index.js??ruleSet[0].use[0]!./resources/js/Pages/Users/Edit.vue?vue&type=script&lang=js:68)
    at callWithErrorHandling (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:6793)
    at setupStatefulComponent (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:6416)
    at setupComponent (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:6372)
    at mountComponent (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:4227)
    at processComponent (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:4202)
    at patch (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:3806)
    at patchKeyedChildren (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:4708)
    at patchChildren (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:4510)
    at processFragment (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:4191)

Inertia's Form Helper