JavaScript Flashcards
What is the purpose of variables?
variables store primitives like numbers, strings and boolean
How do you declare a variable?
var keyword
How do you initialize (assign a value to) a variable?
equal sign
What characters are allowed in variable names?
$, _, letters and digits
Must start with a letter, $ or _
What does it mean to say that variable names are “case sensitive”?
It means capitalized variable names and non-capitalized variable names are different
What is the purpose of a string?
It stores text
What is the purpose of a number?
It stores value
What is the purpose of a boolean?
It stores true or false
What does the = operator mean in JavaScript?
assignment operator
How do you update the value of a variable?
use assignment operator again
What is the difference between null and undefined?
undefined has been assigned but does not have a value. Null is intentionally left blank.
Why is it a good habit to include “labels” when you log values to the browser console?
for clarity and visibility
Give five examples of JavaScript primitives.
numbers, strings, boolean, null and undefined
What data type is returned by an arithmetic operation?
number
What is string concatenation?
adding strings together
What purpose(s) does the + plus operator serve in JavaScript?
arithmetic and concatenation
What data type is returned by comparing two values (, ===, etc)?
Boolean
What does the += “plus-equals” operator do?
addition operator
What are objects used for?
To store multiple properties in one variable name
What are object properties?
data of the object
Describe object literal notation.
starts with variable declaration followed by curly brackets with property names in them.
How do you remove a property from an object?
use delete operator
What are the two ways to get or update the value of a property?
dot notation or bracket notation
What are arrays used for?
To keep lists of data and access them
Describe array literal notation.
brackets and data separated by commas
How are arrays different from “plain” objects?
They are in order and indexed
What number represents the first index of an array?
zero
What is the length property of an array?
it returns how many data are inside the array
How do you calculate the last index of an array?
subtract one from the length of the array since it starts at zero
What is a function in JavaScript?
Reusable code block
Describe the parts of a function definition.
function name, parameter, code block
Describe the parts of a function call.
functionName(argument)
When comparing them side-by-side, what are the differences between a function call and a function definition?
call is using arguments and definition is using parameters
Why are function parameters useful?
Because unlike constant values, we can make changes to that one parameter and rest of the code block will change
What two effects does a return statement have on the behavior of a function?
It returns a value and executes the function
Why do we log things to the console?
To debug and for data accuracy
What is a method?
Method is a function that is a property of an object
How is a method different from any other function?
It is exclusive to the object
How do you remove the last element from an array?
pop() method of array object
How do you round a number down to the nearest integer?
floor) method of Math object
How do you generate a random number?
random() method of Math object
How do you delete an element from an array?
Either shift() or splice() method of array object
How do you append an element to an array?
push() method of array object
How do you break a string up into an array?
split() method of string object
Do string methods change the original string? How would you check if you weren’t sure?
No it does not. Use console log to check.
Roughly how many string methods are there according to the MDN Web docs?
A lot. Maybe like 20 to 30.
Is the return value of a function or method useful in every situation?
No
Roughly how many array methods are there according to the MDN Web docs?
A lot. Maybe like 20 to 30.
What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?
MDN
What is the purpose of an if statement?
Decision making
What are the three logical operators?
And, Or, Not
What is the purpose of a loop?
To repeat our desired action
What is the purpose of a condition expression in a loop?
To eventually stop the loop from running forever
What does “iteration” mean in the context of loops?
To repeat things easily
When does the condition expression of a while loop get evaluated?
Before each repetition starts
When does the initialization expression of a for loop get evaluated?
At the beginning of for loop (only once)
When does the condition expression of a for loop get evaluated?
Before each repetition starts
When does the final expression of a for loop get evaluated?
At the end of each repetition
Besides a return statement, which exits its entire function block, which keyword exits a loop before its condition expression evaluates to false?
break statement
What does the ++ increment operator do?
Increments by 1 and updates
How do you iterate through the keys of an object?
use for in loop (var in object)
