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Web Development > JavaScript > Flashcards

JavaScript Flashcards

1
Q

What is the purpose of variables?

A

A placeholder (container) to temporarily store bits of information/data in memory.

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2
Q

How do you declare a variable?

A

Use a variable keyword (const, let, var) and then assign it a variable name.

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3
Q

How do you initialize (assign a value to a variable)?

A

Use the assignment operator (=).

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4
Q

What characters are allowed in variable names?

A

-Variables must only start with a letter, dollar sign ($), or and underscore ().
-Variables can contain letters, numbers, dollar sign ($), or an underscore().
DO NOT USE a dash (-) or a period (.) in a variable name.
-Variables CANNOT use keywords or reserved words.

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5
Q

What does it mean to say that variable names are “case sensitive”?

A

It means that Score and score would be different variables, but it is bad practice to create two variables that have the same name using different cases.

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6
Q

What is the purpose of a string?

A

Storing and manipulating text data.

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7
Q

What is the purpose of a number?

A

Storing and manipulating numerical data (maths).

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8
Q

What is the purpose of a boolean?

A

A logical data type that can have only the values true or false.
(Booleans allow for making decisions in JavaScript).

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9
Q

What does the = operator mean in JavaScript?

A

Assignment.

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10
Q

How do you update the value of a variable?

A

Reassign it.

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11
Q

What is the difference between null and undefined?

A

Undefined is a variable that refers to something that doesn’t exist, and the variable isn’t defined to be anything. (Accidental emptiness).
-Programmers will NEVER use undefined as a variable.

Null is a variable that is defined but is missing a value. (Purposeful emptiness).
-Programmers will sometimes use null as a variable.

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12
Q

Why is it a good habit to include “labels” when you log values to the browser console?

A

-Make things more clear.
-To help debug.

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13
Q

Give seven examples of JavaScript primitives.

A

-string.
-number.
-boolean.
-undefined.
-null.
-bigint.
-symbol.

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14
Q

What are objects used for?

A

To store multiple pieces of data, that are related to each other.

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15
Q

What are objects properties?

A

A individual piece of named data that stores a value, within an object.

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16
Q

Describe object literal notation.

A

An object literal with key: value pairs is assigned to a variable.

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17
Q

What are the two ways to get or update the value of a property?

A

Dot notation.
Square bracket notation.

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18
Q

What are arrays used for?

A

-Organizing data.

-Working with a list or a set of values
that are related to each other.

-Especially helpful when you do not
know how many items a list will contain.

-Storing a list of information, either order is very important or not important.

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19
Q

Describe array literal notation.

A
  • Give the array a name. (Make a variable).

-Values are then assigned to the array inside a pair of square brackets, and each value is separated by a comma.

-(Array values do not need to be the same data type, but often are).

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20
Q

How are arrays different from “plain” objects?

A

*** Arrays always start with a length (index 0).

  • Arrays are a special type of object. They hold a related set of key/value pairs (like all objects), but the key for each value is its index number.

-Arrays have index numbers for keys.

-Arrays, almost always, contain the same data type.

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21
Q

What number represents the first index of an array?

A

Zero.

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22
Q

What is the length property of an array?

A

-The length property sets or returns the number of elements in an array.

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23
Q

How do you calculate the last index of an array?

A

-Example: array.length - 1.

24
Q

What is a function in JavaScript?

A

A set of actions/instructions that can be reused in the code.

25
Q

Describe the parts of a function definition.

A
  • Function keyword.
  • name of function (optional).
  • Zero or more parameters.
  • Code block.
  • Code within code block.
  • Return (optional).
  • End of code block.
26
Q

Describe the parts of a function call.

A
  • Function name.
  • Arguments.
27
Q

When comparing them side-by-side, what are the differences between a function call and a function definition?

A
  • A function definition has a keyword and a code block, function calls do not.
28
Q

What is the difference between a parameter and an argument?

A
  • Parameters are used as placeholders for variables in the function definition.
  • Arguments are used to input data to the function definition, in the function call.
29
Q

Why are function parameters useful?

A
  • They hold variables (placeholders), which can be used to input data types.
  • Makes functions reusable for different data inputs.
  • Gives functions variance.
30
Q

What two effects does a return statement have on the behavior of a function?

A
  • It returns the result of the function definition to the function call.
  • It can stop the function.
31
Q

Why do we log thins to the console?

A
  • To test/verify code.
  • To bug check.
32
Q

What is a method?

A

A method is a function that is assigned to a property within an object.

33
Q

How is a method different from any other function?

A

It is a function within an object.

** Dot notation is used when a method is called. ***

34
Q

How do you remove the last element from an array?

A

Use the .pop() method.

35
Q

How do you round a number down to the nearest integer?

A

Use the Math.floor() method.

36
Q

How do you generate a random number?

A

Use the Math.random() method.

37
Q

How do you delete an element from an array?

A

Use the .splice() method.

38
Q

How do you break a string up into an array?

A

Use the .split() method.

39
Q

Do string methods change the original string? How would you check if you weren’t sure?

A

Strings are immutable, so it does not change the string stored in memory.

You can console log the string variable.

Check the MDN documentation.

40
Q

Is the return value of a function or method useful in every situation?

A

No, sometimes it’s not.

Ex. You would never save the return value of console.log.

41
Q

What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?

A

MDN

42
Q

Give 6 examples of comparison operators.

A

Strickly equal to ( === )
Strickly not equal to ( !== )
Greater than ( > )
Less than ( < )
Greater than or equal to ( >= )
Less than or equal to ( <= )

43
Q

What data type do comparison expressions evaluate to?

A

Data type: Boolean (true or false).

44
Q

What is the purpose of an ‘if’ statement?

A

Allows for decision making in code.
Creates branching logical paths.

45
Q

Describe the syntax (structure) of an ‘if’ statement.

A
  • ‘If” keyword.
  • Condition(s) within parentheses.
  • Conditional code block for the return.
46
Q

What are the three logical operators?

A
  • Logical ‘And’ (&&).
  • Logical ‘Or’ ( || ).
  • Not operator ( ! ).
47
Q

How do you compare two different expressions in the same condition?

A

Use a logical operator. ( && / || )

48
Q

What is the purpose of a loop?

A

-A tool that allows you do to something over and over again.

  • Repeatable job.
  • Similar to an assembly line.
49
Q

What is the purpose of a condition expression in a loop?

A
  • Creates the condition to end the loop.
  • Exit the loop, when the condition is no longer true.
  • Allows the loop to keep going, but does not increment the loop.
50
Q

What does ‘iteration’ mean in the context of loop?

A
  • Repeatable.
51
Q

When does the condition expression of a while loop get evaluatedA?

A
  • Before each iteration of the code block.
52
Q

When does the initialization expression of a for loop get evaluated?

A
  • ONCE, before anything else.
53
Q

When does the condition expression of a ‘for loop’ get evaluated?

A
  • Before each iteration.
54
Q

When does the final expression of a ‘for loop’ get evaluated?

A
  • After each iteration. (And before the condition).
55
Q

Besides a return statement, which exits it entire function block, which keyword exits a loop before its condition expression evaluates to false?

A
  • Break.
56
Q

What does the ++ increment operator do?

A
  • Increments (adds one to) its operand and returns the value before or after the increment, depending on where the operator is placed.
57
Q

How do you iterate through the keys of an object?

A
  • Use a ‘for…in’ loop.

Web Development (10 decks)

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