From the above answeres, following did not work or less preferable:

• (previous_info | json) != '{}' works only for {} empty case, not for null or undefined case
• Object.getOwnPropertyNames(previous_info).length also did not work, as Object is not accessible in the template
• I would not like to create a dedicated variable this.objectLength = Object.keys(this.previous_info).length !=0;

• I would not like to create a dedicated function

  isEmptyObject(obj) {
     return (obj && (Object.keys(obj).length === 0));
  }
  

Solution: keyvalue pipe along with ?. (safe navigation operator); and it seems simple.

It works well when previous_info = null or previous_info = undefined or previous_info = {} and treats as falsy value.

<div  *ngIf="(previous_info | keyvalue)?.length">

keyvalue - Transforms Object or Map into an array of key value pairs.

?. - The Angular safe navigation operator (?.) is a fluent and convenient way to guard against null and undefined

DEMO: demo with angular 9, though it works for previous versions as well

Use json filter and compare with '{}' string.

<div>
    My object is {{ (myObject | json) == '{}' ? 'Empty' : 'Not Empty' }}
</div>

ng-show example:

<div ng-show="(myObject | json) != '{}'"></div>

Are you ok with moving the equality check to the ng-if?

<div ng-controller="TestController as vm">
  <div ng-if="!equals({}, vm.testObject)">
    Test Object is not empty
  </div>
  <div ng-if="equals({}, vm.testObject)">
    Test Object is empty
  </div>
</div>

Otherwise, provide a helper on the scope

app.controller('TestController', function() {
  var vm = this;

  vm.testObject = {};

  vm.empty = function() {
      return vm.testObject === {};
  };
});

then

<div ng-controller="TestController as vm">
  <div ng-if="!vm.empty()">
    Test Object is not empty
  </div>
  <div ng-if="vm.empty()">
    Test Object is empty
  </div>
</div>

In a private project a wrote this filter

angular.module('myApp')
    .filter('isEmpty', function () {
        var bar;
        return function (obj) {
            for (bar in obj) {
                if (obj.hasOwnProperty(bar)) {
                    return false;
                }
            }
            return true;
        };
    });

usage:

<p ng-hide="items | isEmpty">Some Content</p>

testing:

describe('Filter: isEmpty', function () {

    // load the filter's module
    beforeEach(module('myApp'));

    // initialize a new instance of the filter before each test
    var isEmpty;
    beforeEach(inject(function ($filter) {
        isEmpty = $filter('isEmpty');
    }));

    it('should return the input prefixed with "isEmpty filter:"', function () {
          expect(isEmpty({})).toBe(true);
          expect(isEmpty({foo: "bar"})).toBe(false);
    });

});

regards.

if( myVariable ) 
{ 
    //mayVariable is not : 
    //null 
    //undefined 
    //NaN 
    //empty string ("") 
    //0 
    //false 
}

Always keep in mind that undefined and null are different, when you see undefined it means that a variable was declared but it holds no value in it and null is an actual assignment value. Also undefined is a type and null is an object. So..

 if(!(this.user.data.token == null)); 

Should work for you, if you want to add some other conditions just and the operator || and type next condition.

If you're looking to check for undefined objects you can do something like

this.user.data.token != undefined && ... 

and so on..

If you want to check if object/array is empty, I use:

angular.equals({}, yourObject);
angular.equals([], yourArray);