og-image/public/script.js

const ImagePreview = ({ src, width, height }) => {
    const style = {
        border: '1px solid #ccc',
        borderRadius: '3px',
        boxShadow: '0 4px 4px rgba(0, 0, 0, 0.12)'
    };
    return H('img', { src, width, height, style });
}

const Dropdown = ({ options, value, onchange }) => {
    return H('div',
        { className: 'select-wrapper'},
        H('select',
            { onchange: e => onchange(e.target.value) },
            options.map(o =>
                H('option',
                    { value: o.value, selected: value === o.value },
                    o.text
                )
            )
        ),
        H('div',
            { className: 'select-arrow' },
            '▼'
        )
    );
}

const TextInput = ({ value, onchange }) => {
    return H('div',
        { className: 'input-outer-wrapper' },
        H('div',
            { className: 'input-inner-wrapper' },
            H('input',
                { type: 'text', value, onchange: e => onchange(e.target.value) }
            )
        )
    );
}

const Button = ({ label, onclick }) => {
    return H('button', { onclick }, label);
}

const Field = ({ label, input }) => {
    return H('div',
        { className: 'field' },
        H('label', { className: 'field-label' }, label),
        H('div', { className: 'field-value' }, input),
    );
}

const el = document.getElementById('generated');

const fileTypeOptions = [
    { text: 'PNG', value: 'png' },
    { text: 'JPEG', value: 'jpeg' },
];

const fontSizeOptions = Array
    .from({ length: 10 })
    .map((_, i) => i * 25)
    .filter(n => n > 0)
    .map(n => ({ text: n + 'px', value: n + 'px' }));

const markdownOptions = [
    { text: 'Plain Text', value: '0' },
    { text: 'Markdown', value: '1' },
];

const App = (props, state, setState) => {
    const { fileType = 'png', fontSize = '75px', md = '0', text = 'Hello World', images=['https://assets.zeit.co/image/upload/front/assets/design/now-black.svg'] } = state;
    const url = new URL('https://og-image.now.sh/')
    url.pathname = `${text}.${fileType}`;
    url.searchParams.append('md', md);
    url.searchParams.append('fontSize', fontSize);
    for (let img of images) {
        url.searchParams.append('images', img);
    }
    /*
    let url = `https://og-image.now.sh/${text}.${fileType}?md=${md}&fontSize=${fontSize}`;
    for (let img of images) {
        url += '&images=' + img;
    }
    */
    return H('div',
        H(Field, {
            label: 'File Type',
            input: H(Dropdown, { options: fileTypeOptions, value: fileType, onchange: val => setState({fileType: val}) })
        }),
        H(Field, {
            label: 'Font Size',
            input: H(Dropdown, { options: fontSizeOptions, value: fontSize, onchange: val => setState({fontSize: val}) })
        }),
        H(Field, {
            label: 'Text Type',
            input: H(Dropdown, { options: markdownOptions, value: md, onchange: val => setState({ md: val }) })
        }),
        H(Field, {
            label: 'Text Input',
            input: H(TextInput, { value: text, onchange: val => setState({ text: val }) })
        }),
        ...images.map((image, i) => H(Field, {
            label: `Image ${i + 1}`,
            input: H(TextInput, { value: image, onchange: val => { let clone = [...images]; clone[i] = val; setState({ images: clone }) } })
        })),
        
        H(Field, {
            label: `Image ${images.length + 1}`,
            input: H(Button, {
                label: `Add Image ${images.length + 1}`,
                onclick: () => { setState({ images: [...images, ''] }) }
            }),
        }),
        H(ImagePreview, {
            src: url.href,
            width: 405,
            height: 217
        }),
        H(Field, {
            label: 'URL',
            input: H(TextInput, { value: url.href, onchange: val => { console.log(val) }})
        }),
    )
};

R(H(App), el);