IES: JS-deck 2

Question 1

JS function

Answer 1

• JS is case-sensitive
• Typically, expressions may be enclosed in ()
• JS coding may include keywords, operators, values -fixed and variable-, and expressions -which are basically a mix of all, sometimes, and may equal a single value.
• JS explanatory comments may be added in specific fashion
• For consistency, stick with either (‘) or (“) with string literals in your code

Question 2

JS explanatory comments

Answer 2

• “comment-out” lines of code to prevent their execution when debugging code
• shootCharacter sequences may be placed in code without execution: following a “//” (on the same line) or between “/*” and “*/” (for one or more lines)
• when comment-out coding is used, included character sequences are ignored by any code reader
• Good practice: adding explanatory comments makes your JS code more understandable to others as well as yourself, later

Question 3

JS “abstract”

Answer 3

• JS does not have a built-in abstract keyword
• JS significant: avoid in variable/function names
• In JavaScript, there is no abstract keyword
• JS: achieved using abstract classes & interfaces.
• fundamental concept in object-oriented programming (OOP)
• hiding the implementation details of an object and exposing only the essential features

Question 4

JS “arguments”

Answer 4

• JS keyword
• JS significant: avoid in variable/function names
• Represents the list of parameters passed to the function when calling the function.
• Example

const func = function(p1, p2, p3) {
const param = Array.from(arguments);
console.log(param) // [11, 22, 33]
}
func(11, 22, 33);

Question 5

JS “await”

Answer 5

• JS keyword
• JS significant: avoid in variable/function names
• Used to wait for javascript until the Promise returns its result.
• Ex’s.
  1.)

async function fun() {
let promise = new Promise((resolve, reject) => {
setTimeout(() => resolve(" yes, it is done!"), 100)
});

2.)

let res = await promise; // wait until the promise returns us a value
alert(result); // output give yes, it is done
}
};
fun();

Question 6

JS “boolean”

Answer 6

• JS keyword
• JS significant: avoid in variable/function names
• JS represents a data type that can have one of two values: true or false.

Question 7

JS “break”

Answer 7

• JS keyword
• JS significant: avoid in variable/function names
• used into a loop to break or stop the execution of the loop.
• Example

for(var a=0; a<=10; a++) {
if(a == 5)
break;
document.write("The loop is running for " + a + " times");
}

Question 8

JS “byte”

Answer 8

• JS keyword
• JS significant: avoid in variable/function names
• JS: a group of 8 bits. A bit is the most basic unit and can be either 1 or 0
• not just 8 values between 0 and 1, but 256 (2 to the 8th power)) different combinations (rather permutations) ranging from 00000000 via e.g. 01010101 to 11111111 . Thus, one byte can represent a decimal number between 0(00) and 255.

Question 9

JS “case”

Answer 9

• JS keyword
• JS significant: avoid in variable/function names
• Used in a switch-case construct, where the value of an expression compares with the case clause value and executes the statements associated with the case whose case value is matched.
• 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 10

JS “catch”

Answer 10

• JS keyword
• JS significant: avoid in variable/function names
• Again used in exception handling to handle the error.
• 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 11

JS “char”

Answer 11

• JS keyword
• JS significant: avoid in variable/function names
• reserved keyword in JavaScript that is reserved for “future” use.
• JavaScript doesn’t have a dedicated char data type.
• JS uses string data type for single characters and character sequences
• Strings in JavaScript are immutable: Once created, cannot be modified
• Examples
  1. Access character in a string using its index, which starts from 0

let str = "Hello";
let firstChar = str[0]; // firstChar will be 'H'

OR
2. Create a string containing a single character using single or double quotes.

let singleChar = 'a'; 

Question 12

JS “class*”

Answer 12

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a class.
• Example

public class Employee {
public String efn = "Joseph";
public String eln = "Doe";
}

Question 13

JS “const”

Answer 13

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a constant variable and that cannot be farther reassigned.
• Example
  const age=22;

Question 14

JS “continue”

Answer 14

• JS keyword
• JS significant: avoid in variable/function names
• Used into a loop to continue the loop and skip the following statements inside the loop.
• Example

for(var a=0; a<=10; a++) {
if(a == 5)
continue;
document.write("The loop is running for " + a + " times");
}

Question 15

JS “debugger”

Answer 15

• JS keyword
• JS significant: avoid in variable/function names
• Used to stop the execution of javascript code and call debugging function if define. Debugger keyword word the same as the break.
• Example

var prod = 10 * 10;
debugger;
document.getElementbyId("id").innerHTML = prod;

Question 16

JS “default”

Answer 16

• JS keyword
• JS significant: avoid in variable/function names
• Used in a switch expression to specify the actions to be performed if no case
• 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 17

JS “delete”

Answer 17

• JS keyword
• JS significant: avoid in variable/function names
• Used to remove properties from an object.
• Example

var fruits={f1: "apple", f2: "banana", f3: "orange"};
delete fruits.f1;

Question 17

JS “do”

Answer 17

• JS keyword
• JS significant: avoid in variable/function names
• Used to define a do-while loop.
• Example

var a=1;
do {
document.write("loop is running for " + a + "times</p>");
a++;
}
while(a <= 10);

Question 18

JS “double”

Answer 18

• JS keyword
• JS significant: avoid in variable/function names
• In JavaScript, there is no double keyword
• JavaScript has only one numeric data type: Number representing both integers & floating-point numbers
• Internally, all JS numbers are stored as 64-bit floating-point values according to the IEEE 754 standard - equivalent to the double type in other languages.
• Example

let x = 10;     // integer
let y = 3.14;   // floating-point number
let z = 1e10;   // scientific notation

Question 19

JS “else”

Answer 19

• JS keyword
• JS significant: avoid in variable/function names
• Used in the if-else statement, the else indicates the block of statements to be executed if the expression evaluates false.
• 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!");