[IMP] test_lint, web, point_of_sale: enable no-unsafe-negation rule

This commit also enables the valid-typeof rule which didn't find any
issues

Part-of: odoo/odoo#84530

addons/point_of_sale/static/src/js/db.js

@@ -185,7 +185,7 @@ var PosDB = core.Class.extend({
     add_products: function(products){
         var stored_categories = this.product_by_category_id;
 
-        if(!products instanceof Array){
+        if(!(products instanceof Array)){
             products = [products];
         }
         for(var i = 0, len = products.length; i < len; i++){

addons/web/static/src/legacy/js/core/utils.js

@@ -633,7 +633,7 @@ var utils = Object.assign({
 
         if (typeof(node) === 'string') {
             return sindent + node.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;');
-        } else if (typeof(node.tag) !== 'string' || !node.children instanceof Array || !node.attrs instanceof Object) {
+        } else if (typeof(node.tag) !== 'string' || node.children && !(node.children instanceof Array) || node.attrs && !(node.attrs instanceof Object)) {
             throw new Error(
                 _.str.sprintf(_t("Node [%s] is not a JSONified XML node"),
                             JSON.stringify(node)));

odoo/addons/test_lint/tests/eslintrc

@@ -13,7 +13,9 @@
         "no-restricted-globals": ["error", "event", "self"],
         "no-const-assign": ["error"],
         "no-debugger": ["error"],
-        "no-dupe-class-members": ["error"]
+        "no-dupe-class-members": ["error"],
+        "no-unsafe-negation": ["error"],
+        "valid-typeof": ["error"]
     },
     "globals": {
         "owl": "readonly",