Your PHP code should work on PHP 5.4+.
Your HTML/CSS/JS code should work with at least IE9+, Edge, Firefox 45, and Chrome 29. Mobile-wise: iOS 8.4 and Android Browser 4.4.
Intend with spaces for every language (PHP, HTML, CSS, etc.): 4 spaces for PHP files, 2 spaces for all other filetypes.
Use our .editorconfig file in order to easily configure your editor: https://github.com/PrestaShop/PrestaShop/blob/develop/.editorconfig
You should follow the PSR-2 standard, just like PrestaShop does.
In general, we tend to follow Symfony’s coding standards.
Use HTML 5 tags:
All open tags must be closed in the same file (a <div> should not be opened in header.tpl then closed in footer.tpl). Subtemplates (templates meant to be included in another template) must reside inside a /_partials/ folder.
Use CSS3.
We recommend that you follow the RSCSS structure: http://rscss.io/
Make sure your linter tool follows our .eslint file: https://github.com/PrestaShop/PrestaShop/blob/develop/.eslintrc
If you wish to write ECMAScript 2015 (ES6) code, we advise you to use the Babel compiler: https://babeljs.io/
A good JS practice consists in splitting files per use, and then compiling them into one.
Learn more about the ES2015 standard: https://babeljs.io/docs/learn-es2015/
PrestaShop 1.7 introduces a totally reworked theme system from version 1.6, with the goal of making PrestaShop upgrades easier, and of making it easier/faster to create a brand new theme.
The huge change to the theme system means that there is no easy way to migrate your PrestaShop 1.6 theme to PrestaShop 1.7.
When using the automatic upgrade from PrestaShop 1.6 to 1.7, your theme will be switched to the new default theme, called “Classic”. We therefore advise you to work on your 1.7 theme before you make the switch to PrestaShop 1.7.
Some features have been dropped with PrestaShop 1.7. They were either already deprecated in 1.6, or proved too problematic to maintain.