Computer Programming: Are You Ready To Take The JavaScript Quiz!

1. How many data types are there in javascript?

5

6

There are six data types in JavaScript. These include number, string, boolean, object, null, and undefined. Each data type is used to store different types of values and has its own set of properties and methods. The number data type is used to store numeric values, the string data type is used to store textual values, the boolean data type is used to store true or false values, the object data type is used to store complex data structures, the null data type is used to represent the absence of any object value, and the undefined data type is used to represent variables that have been declared but have not been assigned a value.

Explanation

There are six data types in JavaScript. These include number, string, boolean, object, null, and undefined. Each data type is used to store different types of values and has its own set of properties and methods. The number data type is used to store numeric values, the string data type is used to store textual values, the boolean data type is used to store true or false values, the object data type is used to store complex data structures, the null data type is used to represent the absence of any object value, and the undefined data type is used to represent variables that have been declared but have not been assigned a value.

2. Is "" == 0?

True

False

The expression "" == 0 is comparing an empty string with the number 0. In JavaScript, when comparing values of different types, the interpreter will try to convert one or both of the values to a common type before making the comparison. In this case, the empty string is converted to a number, resulting in 0. Therefore, the expression "" == 0 is true because both sides of the comparison are equal.

Explanation

The expression "" == 0 is comparing an empty string with the number 0. In JavaScript, when comparing values of different types, the interpreter will try to convert one or both of the values to a common type before making the comparison. In this case, the empty string is converted to a number, resulting in 0. Therefore, the expression "" == 0 is true because both sides of the comparison are equal.

3.

var k = {}
k[Symbol('lorem')] = "Max";
k[Symbol('lorem')] = "Payne";
console.log(k[Symbol('lorem')]);

console value is?

"Max"

"Payne"

Undefned

The code creates an empty object `k` and assigns two properties to it using Symbol keys. The first property is assigned the value "Max" and the second property is assigned the value "Payne". When trying to access the value of `k[Symbol('lorem')]`, it will return `undefined` because the Symbol keys are unique and cannot be accessed using any other means except the exact same Symbol key used for assignment. Therefore, the correct answer is "undefined".

Explanation

The code creates an empty object `k` and assigns two properties to it using Symbol keys. The first property is assigned the value "Max" and the second property is assigned the value "Payne". When trying to access the value of `k[Symbol('lorem')]`, it will return `undefined` because the Symbol keys are unique and cannot be accessed using any other means except the exact same Symbol key used for assignment. Therefore, the correct answer is "undefined".

4. What is the output of console.log(0.1 + 0.2 == 0.3)?

True

False

The output of the expression `console.log(0.1 + 0.2 == 0.3)` is `False`. This is because in JavaScript, due to floating point precision, the addition of 0.1 and 0.2 does not result in an exact value of 0.3. Therefore, the comparison `0.1 + 0.2 == 0.3` evaluates to `False`.

Explanation

The output of the expression `console.log(0.1 + 0.2 == 0.3)` is `False`. This is because in JavaScript, due to floating point precision, the addition of 0.1 and 0.2 does not result in an exact value of 0.3. Therefore, the comparison `0.1 + 0.2 == 0.3` evaluates to `False`.

5. What is console.log(1 && 2);

0

1

2

3

The expression "1 && 2" is evaluated using the logical AND operator. In JavaScript, the logical AND operator returns the value of the second operand if the first operand is truthy (not equal to false, 0, "", null, undefined, or NaN), otherwise, it returns the value of the first operand. In this case, both 1 and 2 are truthy values, so the expression evaluates to 2.

Explanation

The expression "1 && 2" is evaluated using the logical AND operator. In JavaScript, the logical AND operator returns the value of the second operand if the first operand is truthy (not equal to false, 0, "", null, undefined, or NaN), otherwise, it returns the value of the first operand. In this case, both 1 and 2 are truthy values, so the expression evaluates to 2.

6. detect the console value of the following line of code.

function Foo(a,b,c){ 
this.x = a; 
this.y = b; 
this.z = c; 
} 
var m = Foo(3,4,5); 
var k = {}; 
Foo.call(k,3,4,5); 
console.log(k); 
console.log(m);

{}, {}

{3,4,5}, {}

{3,4,5}, {3,4,5}

{3,4,5}, undefined

The code snippet defines a constructor function `Foo` that takes three arguments `a`, `b`, and `c`. Inside the function, it assigns the values of `a`, `b`, and `c` to the properties `x`, `y`, and `z` of the newly created object using the `this` keyword.

In the first line after the function definition, `var m = Foo(3,4,5);`, the `Foo` function is called without using the `new` keyword. This means that it is not used as a constructor and does not create a new object. Instead, it simply executes the code inside the function and returns `undefined`. Therefore, `m` is assigned the value `undefined`.

In the next line, `var k = {};`, a new empty object `k` is created.

Then, `Foo.call(k,3,4,5);` is called, which executes the `Foo` function with `k` as the `this` value and passes `3`, `4`, and `5` as arguments. This assigns the values `3`, `4`, and `5` to the properties `x`, `y`, and `z` of `k`.

Finally, `console.log(k);` logs the value of `k`, which is `{3,4,5}`, and `console.log(m);` logs the value of `m`, which is `undefined`.

Explanation

The code snippet defines a constructor function `Foo` that takes three arguments `a`, `b`, and `c`. Inside the function, it assigns the values of `a`, `b`, and `c` to the properties `x`, `y`, and `z` of the newly created object using the `this` keyword.

In the first line after the function definition, `var m = Foo(3,4,5);`, the `Foo` function is called without using the `new` keyword. This means that it is not used as a constructor and does not create a new object. Instead, it simply executes the code inside the function and returns `undefined`. Therefore, `m` is assigned the value `undefined`.

In the next line, `var k = {};`, a new empty object `k` is created.

Then, `Foo.call(k,3,4,5);` is called, which executes the `Foo` function with `k` as the `this` value and passes `3`, `4`, and `5` as arguments. This assigns the values `3`, `4`, and `5` to the properties `x`, `y`, and `z` of `k`.

Finally, `console.log(k);` logs the value of `k`, which is `{3,4,5}`, and `console.log(m);` logs the value of `m`, which is `undefined`.

7.

(function(){ 
var a = b = 3; 
})(); 

console.log(typeof a !== 'undefined'); 
console.log(typeof b !== 'undefined');

what are console values of above?

True, true

True, false

False, true

False, false

In the given code, there is a self-invoking function that declares a variable "a" and assigns it the value of 3. However, the variable "b" is not declared with the "var" keyword, so it becomes a global variable. Therefore, "a" is not accessible outside the function and its type is undefined. On the other hand, "b" is accessible globally and its type is not undefined. Hence, the console values are false for the first statement and true for the second statement.

Explanation

In the given code, there is a self-invoking function that declares a variable "a" and assigns it the value of 3. However, the variable "b" is not declared with the "var" keyword, so it becomes a global variable. Therefore, "a" is not accessible outside the function and its type is undefined. On the other hand, "b" is accessible globally and its type is not undefined. Hence, the console values are false for the first statement and true for the second statement.