click 'back' button will not trigger full page load AFTER refresh

[hasakilol]

I have a SPA website. It has 3 pages: page one(e.g. http://myapp/page1), page two(e.g. http://myapp/page2) and page three(e.g. http://myapp/page3).

Scenario One:
I'm

1. on http://myapp/page1,
2. click a link, navigate to http://myapp/page2
3. then I click Refresh button of browser.
4. click Back button of browser. I find that browser will NOT do a full page load(a full page load will load index.html file) but only do a route change and go to page 1.

For step 4, is this a browser default behavior? or react router behavior?

Scenario Two:
I'm

1. on http://myapp/page1,
2. click a link, navigate to http://myapp/page2
3. I input http://myapp/page3 in address bar of browser and press ENTER.
4. click Back button of browser. I find that browser will DO a full page load(a full page load will load index.html file) and go to page 2.

For step 4, is this a browser default behavior? or react router behavior?