Create your own custom mixin in LoopBack NodeJs

A mixin is nothing more than a method of two parameters:

function(Model, options):

“Model” is the model on which the mixin will be applied
“options” are the options that may be defined in the model.json under the mixins key. To add a mixin you only need to add mixinName: true. If instead of true you provide an object, then this object is the options parameter of the mixin function.

Step-by-step guide:

Following steps involved to create a mixin in loopback:

First create a mixins folder in project/common directory.
Now, create a file mixinName.js (any name) in mixins folder.
Open a file and write a following code:

'use strict';
module.exports = function(Model, options) {
   Model.observe('before save', addConsoleLog);
};
let addConsoleLog = function(ctx, next) {
   if (ctx.instance) {
     
       console.log("Model instance is", ctx.instance);
   }
  
   next();
}

You will add any observer in your custom mixin.

4. After this add your custom mixin in any model json e.g Account.json.

{
   "name": "Account",
   "base": "PersistedModel",
   "idInjection": true,
   "options": {
      "validateUpsert": true
    },
    "mixins": {
      
        mixinName: true
    },
    "properties": {
       "firstName": {
          "type": "string"
       },
      "lastName": {
          "type": "string"
       }
    },
    "validations": [],
    "relations": {},
    "acls": [],
    "methods": {}
}

This is it! Here are the links to the corresponding files in my project: