Working on an overview of all possibilities of adding JavaScript.
Can someone confirm Custom Actions run after JSLinks
By execution order:
Page Scripts
using <script> tags or scriptlink includes.
MasterPage
The MasterPage executes on every SharePoint page.
On Office365/SharePoint Online this method is discouraged by Microsoft (so any Cloud functionalty pushed by Microsoft does not conflict with your code
Page
Same construct as MasterPages, scripts are only loaded on one page
Edit ASPX page in SharePoint Designer (or any text editor)

JSLink injections on WebParts, Views, Forms, Fields
JSLink connection to CSR JS files (but can be any JS file)
SharePoint Online allows for absolute URLs, OnPrem requires URLs with ~token
- http://www.codeproject.com/Articles/610259/SharePoint-Client-Side-Rendering-List-Forms 
- http://www.codeproject.com/Articles/1039724/SharePoint-Client-Side-Rendering-List-Forms-p 
- https://code.msdn.microsoft.com/office/Client-side-rendering-JS-2ed3538a 
- BookMarklet iCSR Link Manager 
 update JSLink settings on WebParts & Views, deploy JS files to Style Library

Calculated Column (View)
(Like the CEWP) Executes JavaScript while the page is loading

Custom Actions
- ASPX Page UserCustomActions 
- https://channel9.msdn.com/Blogs/Office-365-Dev/JavaScript-injection-in-SharePoint-Online-Office-365-Developer-Patterns-and-Practices 
 MSDN: https://msdn.microsoft.com/en-us/library/office/dn913116.aspx?f=255&MSPPError=-2147217396

WebParts on page
CEWP
<script> content
The code is executed while the page is loading, so put the WebPart at the bottom of the page or use jQuery ready function or SharePoints _spBodyOnloadFunctionNames
Without content IN the WebPart, the title can link to a JavaScript in a Library
SEWP

Browser
These scripts (Great for Admin tasks) are not part of SharePoint but can run in the Browser (for the current Browser/User only)
Extension
Browser Extensions (Chrome & FireFox) must be installed
- (Chrome Browser Extension) Cisar 
 Edit CSR files (and create JSLinks) with Live Updating
- (Chrome Browser Extension) Chrome SP Editor 
 Edit SharePoint files, add ScriptLinks to SiteCollection/Webs, manage Web Property Bag
These are powerfull ones, executing script automatically on pages
Console (manual)
Chrome Snippets (manual)
Allow for editting JavaScript against the current SharePoint context.
https://developers.google.com/web/tools/chrome-devtools/debug/snippets/?hl=en
Bookmarklet (manual)
- BookMarklet iCSR Link Manager
 update JSLink settings on WebParts & Views, deploy JS files to Style Library
J1 J5 JW

