Separate base64 from String

Question

Hi,

I have my TinyMCE field,from that iam getting the below "String" value.From that I need to take only encoded base64 part.How can i do it?

Example

var String="<p><img src="data:image/png;base64,iVBORw0KGgoAAAANSUh=" /></p>

<p><img src="data:image/png;base64,/9j/4AAQSkZJRgABAQAAAQABAA=" /><br /><br />---------- Reply message ----------<br />From: [email protected]<br />Date: 04/01/2018 02:50:19 PM<br />Subject: Ticket No: gh<br />To: [email protected]<br />";

output will be

iVBORw0KGgoAAAANSUh=

/9j/4AAQSkZJRgABAQAAAQABAA=