When i try to replace string 0,50 with javascript 'mydiv' has been deleted/moved

Example

<div id="para1"><div class="mydiv"></div>0,50</div>

When i try to replace 0,50 by 80 i do :

document.getElementById("para1").innerText = "80"

or with jQuery

$("#para1").text("80")

then the result is :

<div id="para1">80</div>

during the operation it delete <div class="mydiv"></div>

How can i do to keep structure of html and result like this :

<div id="para1"><div class="mydiv"></div>80</div>