IES: JS-deck 4

Question 1

JS “native”

Answer 1

• JS keyword
• JS significant: avoid for variable/function names
• In JavaScript, there’s no native keyword: the term “native JavaScript” is often used to describe:
• Built-in functionalities:
• Features and objects that are part of the JavaScript language itself or are provided by the JavaScript engine without requiring external libraries or frameworks.
• Vanilla JavaScript: Code written without the use of external libraries or frameworks.

Question 2

JS “new”

Answer 2

• JS keyword
• JS significant: avoid in variable/function names
• Used to create an object.
• Example
  Employee obj = new Employee ();

Question 3

JS “null”

Answer 3

• JS keyword
• JS significant: avoid in variable/function names
• Used to represent a special data type no value.
• Example
  ~~~
  var age = null;
  alert(age);
  ~~~

Question 4

JS “package”

Answer 4

• JS keyword
• JS significant: avoid in variable/function names
• Used to identify java classes and to execute the java method in a javascript.
• Example
  inBlock['package'] = something;

Question 5

JS “private”

Answer 5

• JS keyword
• JS significant: avoid in variable/function names
• IS an access modifier can be used with attributes, classes, constructors and methods which make it not accessible to other classes.
• Example
  ~~~
  public class Employee {
  private String efn = “Joseph”;
  }
  class MainClass {
  public static void main(String[] args) {
  Employee obj = new Employee ();
  System.out.println(“Name= “ + obj.efn + “ “ + obj.lname);// gives error
  }
  }
  ~~~

Question 6

JS “protected”

Answer 6

• JS keyword
• JS significant: avoid in variable/function names
• An access modifier can be used with attributes, classes, constructors and methods which make it not accessible to other classes.
• Example

Question 7

JS “public”

Answer 7

• JS keyword
• JS significant: avoid in variable/function names
• In JS, the concept of public is not a keyword: by default, all members (properties and methods) of a class are public cooling: you don’t need any special keyword to declare them.
• Example
  ~~~
  class Person {
  constructor(name, age) {
  this.name = name; // Public property
  this.age = age; // Public property
  }greet() { // Public method
  console.log(Hello, my name is ${this.name});
  }
  }

const john = new Person(“John”, 30);
console.log(john.name); // Accessing public property
john.greet(); // Calling public method
~~~

Question 8

JS “return”

Answer 8

• JS keyword
• JS significant: avoid for variable/function names
• In JavaScript, the return keyword is used to specify the value that a function should output or “return” back to the caller.
• When a return statement is encountered within a function, the function immediately stops executing, and the specified value (if any) is sent back to the code that called the function.
• You can use return to return a value from a function. This allows you to use the result of the function’s computations in other parts of your code.
• If you don’t specify a value after the return keyword, or if you omit the return statement altogether, the function will return undefined.
• Example
  ~~~
  function addNumbers(num1, num2) {
  return num1 + num2;
  }

let result = addNumbers(3, 5);
console.log(result); // Output: 8
~~~

Question 9

JS “short”

Answer 9

• JS keyword
• JS significant: avoid for variable/function names
• Belongs to the so-called future keywords by the ECMAScript specification. Has no special functionality at present but might at some future time.
• In ECMAScript 5/6, short was removed from the list of reserved words. Nonetheless for compatibility with older browsers not implementing either, you shouldn’t use it anyway.

Question 10

JS “static”

Answer 10

• JS keyword
• JS significant: avoid for variable/function names
• Used to define a static method in a class. Static methods are those methods that are not called on the object.
• Example
  ~~~
  class Employee extends Person {
  constructor(name, eid, salary) {
  super(name);
  }
  static disp()
  {
  return “This is static method “
  }
  }
  document.writeln( Employee.disp() );
  ~~~

Question 11

JS “super”

Answer 11

• JS keyword
• JS significant: avoid in variable/function names
• Used to call function or method of a parent class.
• Example
  super.disp(); //the disp is a method of a parent class

Question 12

JS “switch”

Answer 12

• JS keyword
• JS significant: avoid in variable/function names
• Used in a switch-case construct, where switch evaluates an expression.
• Example
  ~~~
  var date = new Date();
  switch(date.getDay()) {
  case 6:
  alert(“This is weekend.”);
  break;
  case 0:
  alert(“This is weekend.”);
  default:
  alert(“Looking for a weekend.”);
  break;
  }
  ~~~

Question 13

JS “synchronized”

Answer 13

• JS keyword
• JS significant: avoid for variable/function names
• JavaScript does not have a synchronized keyword
• JavaScript is single-threaded. This eliminates the need for explicit synchronization

Question 14

JS “this”

Answer 14

• JS keyword
• JS significant: avoid in variable/function names
• Used to refer to the current object.
• Example
  ~~~
  class Employee extends Person {
  constructor(name, eid, salary) {
  super(name);
  }
  get incsalary() {
  return this.salary * 0.2;
  }
  }
  ~~~

Question 15

JS “throw”

Answer 15

• JS keyword
• JS significant: avoid in variable/function names
• Used in a try block to explicitly throw an exception object.
• Example
  ~~~
  Var i=1
  try {
  if(i == “”) throw “is Empty”;
  if(x > 0) throw “positive”;
  if(x < 0) throw “negative”;
  }
  catch(msg) {
  message.innerHTML = “Input “ + msg;
  }
  ~~~

Question 16

JS “throws”

Answer 16

• JS keyword
• JS significant: avoid for variable/function names
• In JavaScript, there is no throws keyword.
• JavaScript uses throw for error handling (used to explicitly throw an exception (error) in your code)

Question 17

JS “transient”

Answer 17

• JS keyword
• JS significant: avoid for variable/function names
• In JS, there is no transient keyword: JS doesn’t have the concept of serialization: when you want to store or transmit data in JS, you typically use JSON.
• if you want to exclude certain properties from a JSON representation of an object in JS,
• Example
  Manually delete them:
  ~~~
  const obj = {
  name: “John”,
  age: 30,
  password: “secret”
  };

delete obj.password; // Remove the password property

const jsonString = JSON.stringify(obj); // Convert to JSON
~~~

Use a custom serialization function:
~~~
function customToJSON(obj) {
const result = {};
for (const key in obj) {
if (key !== “password”) {
result[key] = obj[key];
}
}
return result;
}

const jsonString = JSON.stringify(obj, customToJSON);
~~~

Question 18

JS “true”

Answer 18

• JS keyword
• JS significant: avoid in variable/function names
• Used to store or represent primitive data type Boolean ‘true’.
• Example
  var inp = true;

Question 19

JS “try”

Answer 19

• JS keyword
• JS significant: avoid in variable/function names
• Used for exception handling to check a block of code for errors.
• Example
  ~~~
  Var i=1
  try {
  if(i == “”) throw “is Empty”;
  if(x > 0) throw “positive”;
  if(x < 0) throw “negative”;
  }
  catch(msg) {
  message.innerHTML = “Input “ + msg;
  }
  ~~~

Question 20

JS “typeof”

Answer 20

• JS keyword
• JS significant: avoid in variable/function names
• Which used to return the data type of an operand.
• Example
  typeof("hello") // output as string