CODE EXAMPLE FOR JAVASCRIPT

full width of image and maintain aspect ratio react native

render() {
    let image = this.props.requireSource;
    const { width, height } = Image.resolveAssetSource(image);
    const ratio = height / width;
    const SCREEN_WIDTH = Dimensions.get('window').width;

    return (
        <Image source={image} style={{width: SCREEN_WIDTH, height: SCREEN_WIDTH*ratio}} resizeMode="contain"/>
    );
}