app not installed as package appears to be invalid.

 

Solution 

Step 1 : Start Android Studio 

Step 2 : Go to Build -> Build Bundles 

Step 3 : Select Build APK

Step 4 : Build APK file

How to Rename an Object's Key in JavaScript | Demo | Example

Demo URl

Code Example Here

 function renameKeys(obj, newKeys) {

  const keyValues = Object.keys(obj).map(key => {
    const newKey = newKeys[key] || key;
    return { [newKey]: obj[key] };
  });
  return Object.assign({}, ...keyValues);
}

Uses

 const obj = { a: "1", b: "2" };

const newKeys = { a: "A", c: "C" };
const renamedObj = renameKeys(obj, newKeys);
console.log(renamedObj);

// {A:"1", b:"2"} 

How many ways to create Objects in JavaScript

 We can 5 ways to create objects in JavaScript.

Lets understand how to Create it...

Demo URL

'use strict';

Example 1

var fruit = {};

fruit.name = 'Mango';

fruit.color = 'Yellow';

console.log(`fruit name ${fruit.name} and color is ${fruit.color}`);

Example 2

var fruit2 = { name: 'Mango', color: 'Yellow' };

console.log(`fruit name ${fruit2.name} and color is ${fruit2.color}`);

function Fruit(name, color) {

  (this.name = name), (this.color = color);

}

Example 3

var fruit3 = new Fruit('Mango', 'Yellow');

Example 4

var fruit4 = new Fruit('Donut', 'Sprinkled Yellow');

console.log(`fruit name ${fruit3.name} and color is ${fruit3.color}`);

console.log(`fruit name ${fruit4.name} and color is ${fruit4.color}`);

console.log(`Check fruit3 proto ${Fruit.prototype === fruit3.__proto__}`);

// console.log(`Property descriptor

// ${JSON.stringify(Object.getOwnPropertyDescriptor(fruit,'name'))}`)

Example 5

var fruit5 = Object.create(Object.prototype, {

  name: {

    value: 'Mango',

    enumerable: true,

    writable: true,

    configurable: true,

  },

  color: {

    value: 'Yellow',

    enumerable: true,

    writable: true,

    configurable: true,

  },

});

console.log(`fruit name ${fruit5.name} and color is ${fruit5.color}`);

console.log(`Check fruit3 proto ${fruit.prototype === fruit5.__proto__}`);

var fruit6 = Object.create(Object.prototype, {

  name: {

    value: 'Mango',

    enumerable: true,

    writable: true,

    configurable: true,

  },

  color: {

    value: 'Yellow',

    enumerable: true,

    writable: false,

    configurable: true,

  },

});

fruit6.name = 'Sausages';

//compile error comment it later

//fruit6.color="Red";

for (var props in fruit6) {

  console.log(`${props} : ${fruit6.color}`);

}

console.log(

  `Fruit name ${fruit6.name} and color is ${

    fruit6.color

  } and proto ${JSON.stringify(fruit6.__proto__)}`

);

//Getter Setter

var fruit7 = {

  color: 'Yellow',

  get fruitcolor() {

    return this.color;

  },

  set fruitcolor(val) {

    this.color = val;

  },

};

console.log(`Fruit default color is ${fruit7.fruitcolor}`);

fruit7.fruitcolor = 'Yellow';

console.log(`Fruit changed color is ${fruit7.fruitcolor}`);

console.log(`Check Fruit3 proto ${Fruit.prototype === fruit3.__proto__}`);

What is the difference between Components and Directives?

 
Demo URL

@Components	@Directives
For register component we use @Component meta-data annotation.	For register directives we use @Directive meta-data annotation.
Component is a directive which use shadow DOM to create encapsulate visual behavior called components. Components are typically used to create Ul widgets.	Directives are used to add behavior to an existing DOM element.
Component is used to break up the application into smaller components.	Directive is used to design reusable components.
Only one component can be present per DOM element.	Many directive can be used in a per DOM element
Component is used to define pipes	You can't define Pipes in a directive.
@View decorator or templateurl template are mandatory in the component.	Directives don't have a View.

What is the difference between constructor and ngOnInit? | Demo | Example

Demo URL

Constructor	ngOninit
A constructor is not the concept of Angular. It is the concept of JavaScript's class.	ngOninit is the second stage of Angular component lifecycle hook whenever is called when angular is done which creating the component.
Constructor is best place to add all dependencies	ngOninit function which guarantees you that the component has already been created.
Constructor is automatically called at the time of creating the object of the class.	Invoked by Angular when component is initialized
Used for Injecting dependencies	Actual business logic performed
we should use constructor() to setup Dependency Injection	is a better place to write "actual work code" that we need to execute as soon as the class is instantiated.