JavaScript: document.documentElement.innerHTML not showing all the elements

I'm trying to figure out how to get all the elements of html. For example if I load this google page google search I'll see this result:

I see the source code for that particular section of the page I see this:

<a href="https://www.macworld.com/article/3331839/iphone-2019-rumors-everything-you-need-to-know.html" onmousedown="return rwt(this,'','','','38','AOvVaw07dY5FgPEzcYsd8enm-9gs','','2ahUKEwicoNi4yPjhAhVdCTQIHVxICj4QFjAlegQIABAB','','',event)">
<h3 class="LC20lb">iPhone 2019 rumors: Everything you need to know | Macworld</h3><br><div class="TbwUpd">
<cite class="iUh30">https://www.macworld.com/.../iphone-2019-rumors-everything-you-need-to-know.ht...</cite></div></a>

But if use document.documentElement.innerHTML the output would be this:

<div class="g"><h3 class="r">
<a href="/url?q=https://www.macworld.com/article/3331839/iphone-2019-rumors-everything-you-need-to-know.html&amp;sa=U&amp;ved=0ahUKEwiU__rUy_jhAhWIHzQIHTrGBzIQFghLMAo&amp;usg=AOvVaw2C3PdwxIaeNuukMVSwC-5g">
<b>iPhone 2019</b> rumors: Everything you need to know | Macworld</a>
</h3><div class="s"><div class="hJND5c" style="margin-bottom:2px">

My question to you guys why the difference between seen the source code and running document.documentElement.innerHTML?

Also using javascript how can see or query an element like this:

<a href="https://www.macworld.com/article/3331839/iphone-2019-rumors-everything-you-need-to-know.html" onmousedown="return rwt(this,'','','','38','AOvVaw07dY5FgPEzcYsd8enm-9gs','','2ahUKEwicoNi4yPjhAhVdCTQIHVxICj4QFjAlegQIABAB','','',event)">
<h3 class="LC20lb">iPhone 2019 rumors: Everything you need to know | Macworld</h3><br><div class="TbwUpd">
<cite class="iUh30">https://www.macworld.com/.../iphone-2019-rumors-everything-you-need-to-know.ht...</cite></div></a>

I'll really appreciate your help.

from JavaScript: document.documentElement.innerHTML not showing all the elements