IES: JS-deck 3

Question 1

JS “enum”

Answer 1

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a predefined list.
• Example
  ~~~
  const fruits={
  APPLE: ‘apple’,
  BANANA: ‘banana’,
  Orange: ‘orange’,
  }
  let fruit =fruits.APPLE
  if(!fruit){
  throw new Error(‘ fruit is not defined ‘)
  }
  switch( fruit ){
  case fruit.APPLE: alert(“This is an apple.”);
  break;
  case fruit.BANANA: alert(“This is a banana.”);
  break;
  case fruit.ORANGE: alert(“This is an orange.”);
  }
  ~~~

Question 2

JS “eval”

Answer 2

• JS keyword
• JS significant: avoid in variable/function names
• Used to evaluate a specified string. The eval use as a global function eval().
• Example
  ~~~
  function fun( ) {
  var str1=2;
  var str1=3;
  var res = eval(new String(str1 + str2));
  document.write(res);
  }
  fun();
  ~~~

Question 3

JS “export”

Answer 3

• JS keyword
• JS significant: avoid in variable/function names
• Used to export objects, functions or values from the module so that can be used in another program with the help of import statement.
• Example
  ~~~
  export let var fruits = [“apple”, “banana”, “orange”];// export an array
  export const fruit= “apple”;// export a constant
  ~~~

Question 4

JS “extends”

Answer 4

• JS keyword
• JS significant: avoid in variable/function names
• Used in class declarations to create a class that inherits another class.
• Example
  ~~~
  class Employee extends Person {
  constructor(name, eid, salary) {
  super(name);
  }
  get incsalary() {
  return this.salary * 0.2;
  }
  }
  ~~~

Question 5

JS “false”

Answer 5

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

Question 6

JS “final”

Answer 6

• JS keyword
• JS significant: avoid in variable/function names
• JavaScript does not have a final keyword
• Achieve similar behavior using const to declare variables that hold primitive values (numbers, strings, booleans) that shouldn’t be reassigned

Question 7

JS “finally”

Answer 7

• JS keyword
• JS significant: avoid in variable/function names
• Used in exception handling, finally block of code always execute regardless of whether the error is generating or not.
• 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;
  }
  finally
  {
  alert(“This is a finally code, which always execute.”);
  ~~~

Question 8

JS “float”

Answer 8

• JS keyword
• JS significant: avoid in variable/function names
• In JavaScript, a reserved keyword, but it’s not used to define a floating-point data type
• This data type is used to represent numbers that have a fractional part or to represent very large or small numbers, where fixed-point representation would result in an impractical number of digits.

Question 9

JS “for”

Answer 9

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a loop, for loop to repeatedly execute a block of code until a condition true.
• Example
  ~~~
  for(var a=0; a<=10; a++) {
  document.write(“The loop is running for “ + a + “ times”);
  }
  ~~~

Question 10

JS “function”

Answer 10

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a function to execute a block of code.
• Example
  ~~~
  var func = function(){
  return “Hello”;
  }
  alert(func());
  ~~~

Question 11

JS “goto”

Answer 11

• JS keyword
• JS significant: avoid for variable/function names
• return execution control to a specific location
• Ex.
  ~~~
  var no=0;
  sposition
  document.write(“ something print here “);
  no++;
  if(no < 10) goto sposition;
  ~~~

Question 12

JS “if”

Answer 12

• JS keyword
• JS significant: avoid for variable/function names
• Used to define a conditioned construct. if the statement is used to run a block of code if the condition is true.
• Example
  ~~~
  var date = new Date();
  var day = date.getDay(); // Sunday Saturday : 0 6
  if(day==5) {
  alert(“This is weekend!”);
  } else {
  alert(“This is non-weekend!”);
  ~~~

Question 13

JS “implements”

Answer 13

• JS keyword
• JS significant: avoid in variable/function names
• Used to implement the interface in a class.
• Example
  ~~~
  interface car
  method drive(whichSpeed)
  method break( )
  class car1 implements car
  ~~~

Question 14

JS “import”

Answer 14

• JS keyword
• JS significant: avoid in variable/function names
• Used to import the module in the javascript program.
• Example
  import * as alias from 'https://cdn.educba.com/modules/mymodule.js';

Question 15

JS “in”

Answer 15

• JS keyword
• JS significant: avoid for variable/function names
• It is an operator returns true if the specified property is present in the specified object, else it returns false.
• Example
  ~~~
  var fruits={f1: “apple”, f2: “banana”, f3: “orange”};
  // output as true expected
  console.log(‘apple’ in fruits);
  ~~~

Question 16

JS “instanceof”

Answer 16

• JS keyword
• JS significant: avoid in variable/function names
• Returns true if the object is an instance of the class, otherwise false
• Example
  ~~~
  var fruits=[“apple”, “banana”, “orange”];
  // Returns true
  fruits instanceof Object;
  // Returns true
  fruits instanceof Array;
  // Returns false
  fruits instanceof String;
  ~~~

Question 17

JS “int”

Answer 17

• JS keyword
• JS significant: avoid for variable/function names
• In JavaScript, there is no int keyword: JavaScript has only one numeric data type: number.
• This data type represents both integers and floating-point numbers.

Question 18

JS “interface”

Answer 18

• JS keyword
• JS significant: avoid in variable/function names
• Used to define an interface (interface contains all abstract methods).
• Example
  ~~~
  interface car
  method drive(whichSpeed)
  method break( )
  class car1 implements car
  {
  // Class code here
  }
  ~~~

Question 19

JS “let”

Answer 19

• JS keyword
• JS significant: avoid for variable/function names
• Used to declare a variable limited to a scope of a block of code, unlike a variable declared by the var keyword.
• Example
  let var fruits = ["apple", "banana", "orange"];

Question 20

JS “long”

Answer 20

• JS keyword
• JS significant: avoid in variable/function names
• In JS, there is no long keyword:
  1. JS uses a single number type representing integers and floating-point numbers providing a wide range of values
  2. If working beyond the range of the number type, JS offers BigInt (create: 1. append n to the end of an integer literal; 2. use the BigInt() constructor)