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Astro Utils

Binding & Validation

Introduction

With Astro Forms you can easily create forms with data binding and validation. It also provides a simple way to handle form submissions and preserve state between postbacks.

Data Binding

Astro Forms supports two-way data binding. This means that you can bind a form field to a property on Bind instance and the value of the property will be updated when the field changes and vice versa.

Example

---
import { Bind, BindForm, BButton, BInput } from "@astro-utils/forms/forms.js";
import Layout from "../layouts/Layout.astro";


type Form = {
    name: string;
    age: number;
}


const form = Bind<Form>();


let showSubmitText: string;
function formSubmit(){
    showSubmitText = `You name is ${form.name}, you are ${form.age} years old. `;
    form.age++;
}
---
<Layout>
    <BindForm bind={form}>
        {showSubmitText}


        <h4>What you name*</h4>
        <BInput type="text" name="name" maxlength={20} required/>


        <h4>Enter age*</h4>
        <BInput type="int" name="age" min={10} required/>


        <BButton onClick={formSubmit} whenFormOK>Submit</BButton>
    </BindForm>
</Layout>

In this example, the Bind instance is bound to the form fields.

  • When the user changes the value of the name or age fields and submit, the Bind instance will be updated.
  • The formSubmit function will be called when the user clicks the Submit button and the form is valid.
  • After formSubmit the age property will be incremented and the showSubmitText will be updated.

View State

Astro Forms also supports view state. This means that the values of the form fields will be preserved between postbacks.

Example

---
type Form = {
    counter: number;
}


const form = Bind<Form>({counter: 0});


function incCounter(){
    form.counter++;
}
---
<Layout>
    <BindForm bind={form}>
        Counter: {form.counter}


        <BButton onClick={formSubmit}>Increase counter</BButton>
    </BindForm>
</Layout>

What happens here is that the counter property of the Bind instance will be incremented every time the user clicks the Increase counter button.

The Bind state will persist between postbacks, by storing the data on the client side compressed and encrypted.

Valid values

The state of the Bind instance must be serlizable, but you can use more then just JSON.

You can use any valid SuperJSON value in the Bind instance. Meaning also Date, Map, URL, Set, RegExp, BigInt, undefined are supported.

Button State

You can use state per BButton component. You can also change the BButton props easily each time the button is clicked.

Special props:

  • state: any - store state per button
  • extra: any - store extra data per button (cannot be changed in the onClick function)
  • innerText: string - the text of the button (overides the children)
  • innerHTML: string - the HTML of the button (overides the children)
  • remove: boolean - remove the button from the HTML
---
import { BButton, Bind, BindForm } from '@astro-utils/forms/forms.js';
import Layout from '../layouts/Layout.astro';


const colors = ['red', 'green', 'blue', 'yellow', 'purple', 'orange', 'pink', 'black', 'white', 'gray'];


function changeColor() {
    this.state.color++;


    if (this.state.color >= colors.length) {
        this.state.color = this.extra;
    }
    this.style = `color: ${colors[this.state.color]}`;
}
---


<Layout>
    <BindForm>
        {
            colors.map((_, i) => (
                <BButton onClick={changeColor} extra={i} state={{ color: i }}>
                    Button {i}
                </BButton>
            ))
        }
    </BindForm>
</Layout>

In this example, the changeColor will change the button color each time it is clicked for a different color in the colors array.

If the button is clicked more times then the length of the colors array, it will start from the beginning.

Initial state

Initial state

After some clicks

After clicks