function base64ToUint8Array( str ) {
	var bytes;
	var v;
	var i;

	v = atob( str );
	if ( v === null ) {
		return null;
	}
	bytes = new Uint8Array( v.length );
	for ( i = 0; i < v.length; i++ ) {
		bytes[ i ] = v.charCodeAt( i );
	}
	return bytes;
}
Converts a base64-encoded string to a Uint8Array.

@param {string} str - base64-encoded string
@returns {(Uint8Array|null)} output array

@example
var string2buffer = require( '@stdlib/buffer/from-string' );

var str = string2buffer( 'Hello World!' ).toString( 'base64' );
// returns 'SGVsbG8gV29ybGQh'

var out = base64ToUint8Array( str );
// returns <Uint8Array>[ 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33 ]