[IMP] website, *: lazy load most frontend javascript

* web, survey

This commit takes advantage of the other commits of this PR to enable
lazy loading for most frontend javascript:

1) Extract the minimum part of the assets common:
- promises library and polyfill
- boot.js

2) Create "assets_common_lazy" which is "assets_common" - "minimum"

3) Include the "minimum" assets in frontend layouts using "defer"
   loading and "assets_common_lazy" using "lazy" loading

4) Create a script to do the actual lazy loading in a "minimum" frontend
   assets

5) Lazy load the current frontend / website editor assets

Part of https://github.com/odoo/odoo/pull/32181
task-1961045

1 files changed, 42 insertions, 0 deletions

diff --git a/addons/web/static/src/js/public/lazyloader.js b/addons/web/static/src/js/public/lazyloader.js
new file mode 100644
index 00000000000..7c873e1938d
--- /dev/null
+++ b/addons/web/static/src/js/public/lazyloader.js
@@ -0,0 +1,42 @@
+odoo.define('web.public.lazyloader', function (require) {
+'use strict';
+
+var doResolve = null;
+var _allScriptsLoaded = new Promise(function (resolve) {
+    if (doResolve) {
+        resolve();
+    } else {
+        doResolve = resolve;
+    }
+});
+
+window.addEventListener('load', function () {
+    setTimeout(_loadScripts, 0);
+});
+
+function _loadScripts(scripts, index) {
+    if (scripts === undefined) {
+        scripts = document.querySelectorAll('script[data-src]');
+    }
+    if (index === undefined) {
+        index = 0;
+    }
+    if (index >= scripts.length) {
+        if (typeof doResolve === 'function') {
+            doResolve();
+        } else {
+            doResolve = true;
+        }
+        return;
+    }
+    var script = scripts[index];
+    script.addEventListener('load', _loadScripts.bind(this, scripts, index + 1));
+    script.src = script.dataset.src;
+    script.removeAttribute('data-src');
+}
+
+return {
+    loadScripts: _loadScripts,
+    allScriptsLoaded: _allScriptsLoaded,
+};
+});