Svelte component library using Yup for form validation.
$ npm i svelte-yup --save-dev
$ npm i yup
<script>
    import * as yup from 'yup';
    import {Form, Message} from 'svelte-yup';
    let schema = yup.object().shape({
        name: yup.string().required().max(30).label("Name"),
        email: yup.string().required().email().label("Email address"),
    });
    let fields = {email: "", name: ""};
    let submitted = false;
    let isValid;
    function formSubmit(){
        submitted = true;
        isValid = schema.isValidSync(fields);
        if(isValid){
            alert('Everything is validated!');
        }
    }
</script>
<Form class="form" {schema} {fields} submitHandler={formSubmit} {submitted}>
    <input type="text" bind:value={fields.name} placeholder="Name">
    <Message name="name" />
    <input type="text" bind:value={fields.email} placeholder="Email address">
    <Message name="email" />
    <button type="submit">Submit</button>
</Form>
Example:
<script>
...
import {Message, isInvalid} from 'svelte-yup';
...
$: invalid = (name)=>{
    if(submitted){
        return isInvalid(schema, name, fields);
    }
    return false;
}
...
</script>
<input type="text" class:invalid={invalid("name")} bind:value={fields.name} placeholder="Name">
<style>
.invalid {
    border-color: red !important;
}
</style>
Example below to put all messages in one place by AllMessages component.
import {AllMessages} from 'svelte-yup';
<AllMessages />
<Form ... color="#b00020">
| name | props | description | 
|---|---|---|
| Form | schema,fields,submitHandler,submittedandcolor | |
| Message | name | Error message of a field name by nameprop. name should be the schema field name (no label name) | 
| AllMessages | Puts all field messages in one place | 
isInvalid(schema:Object, name:String, fields:Object) 
...
let btnDisabled = false;
$: if(submitted){
    btnDisabled = true;
    isValid = schema.isValidSync(fields);
    if(isValid){
        btnDisabled = false;
    }
}
...
<button type="submit" disabled={btnDisabled}>Submit</button>
Kamyar Lajani
MIT