JavaScript - Determine whether the cursor is a the beginning of the text contained in a container, ignoring whitespace

Question

I am attempting to determine whether the cursor is at the beginning of a container (where contenteditable is true), ignoring whitespace or HTML elements that comes first. For instance:

<div class="layout-container" contenteditable="true">
    <div class="slice-content">
        <p>       Hello World</p>
    </div>
</div>

<div class="layout-container" contenteditable="true">
    <div class="slice-content">
        <p>Hello World</p>
    </div>
</div>

<div class="layout-container" contenteditable="true">
    <div class="slice-content">
        <p>  <span style="font-weight: normal;">Hello</span> World</p>
    </div>
</div>

Regardless of which ones of these is used to create the following:

I would still want it to return 0.

Currently, I am using the following:

window.getSelection().getRangeAt(0).startOffset;