JavaScript Flashcards
What is the purpose of variables?
To store data/information
How do you declare a variable?
declaring the variable and giving it a name
How do you initialize (assign a value to) a variable?
by the ‘=’ (assignment operator) and giving it a value
What characters are allowed in variable names?
letters , $ , _ (underscore) , and numbers but can’t start with numbers
What does it mean to say that variable names are “case sensitive”?
capital and lowercase letters affect the name. You can have variables spelled the same but with different capitalization
What is the purpose of a string?
storing text / using any series of characters
What is the purpose of a number?
to store numbers for calculations / do math / represent numerical values
What is the purpose of a boolean?
it only has 2 values / used to determine what part of a script should run
What does the = operator mean in JavaScript?
Assignment operator / used to assign variables to data
What is the difference between null and undefined?
null is intentional / while undefined is something you didn’t calculate
Why is it a good habit to include “labels” when you log values to the browser console?
so you know what you are logging
Give five examples of JavaScript primitives.
undefined, null, boolean, string, number
What data type is returned by an arithmetic operation?
number
What is string concatenation?
combining 2 or more strings
What purpose(s) does the + plus operator serve in JavaScript?
it is an arithmetic operator and you can use it with adding numbers / also concatenate strings
What data type is returned by comparing two values (, ===, etc)?
a boolean
What does the += “plus-equals” operator do?
it adds the value on the right to the left value
What are objects used for?
group together a set of variables and functions
combining like data (cars, person)
What are object properties?
variable that is part of an object
Describe object literal notation.
easiest way to create an object
variable declaration with name and assign it a value of {} with properties and methods inside
How do you remove a property from an object?
delete objectName followed by the property name
What are the two ways to get or update the value of a property?
the dot notation and bracket notation
What are arrays used for?
to store a list of items / values
Describe array literal notation.
var name = [] / var variable with the name assignment operator with square brackets and properties inside
What number represents the first index of an array?
0
What is the length property of an array?
property that tells you how long an array is
How do you calculate the last index of an array?
by subtracting 1 from the length
How are arrays different from “plain” objects?
they maintain order
What is a function in JavaScript?
a reusable line of code that can do multiple things
Describe the parts of a function definition.
function keyword to create the function
optional name
parenthesis with an parameter or if multiple separate with comma
start of the code block with {
optional return statement at the end
end of the code block with }Describe the parts of a function call.
name of the function with () and the argument/arguments inside
When comparing them side-by-side, what are the differences between a function call and a function definition?
the function call is barebones in that it is only the name of the function and arguments
What is the difference between a parameter and an argument?
arguments are the ones that go into calling the functions
parameters go in the function definition and are only placeholders
Why are function parameters useful?
they are placeholders so you can input so you can input your own arguments and be able to use the functions multiple times
What two effects does a return statement have on the behavior of a function?
Causes the function to produce a value we can use in our program.
Prevents any more code in the function’s code block from being run.
Why do we log things to the console?
to be able to check if we are getting the return we want
What is a method?
A JavaScript method is a property of an object that contains a function definition. Methods are functions stored as object properties.
How is a method different from any other function?
A function is a block of code written to perform some specific set of tasks.
A JavaScript method is a property of an object that contains a function definition.
How do you remove the last element from an array?
.pop() method
How do you round a number down to the nearest integer?
Math.round()
How do you generate a random number?
Math.random()
How do you delete an element from an array?
.pop() , .shift() , .splice()
How do you append an element to an array?
.push() , .unshift()
How do you break a string up into an array?
.split()
Do string methods change the original string? How would you check if you weren’t sure?
yes by console.log()
Roughly how many string methods are there according to the MDN Web docs?
59 / alot
Is the return value of a function or method useful in every situation?
no / you dont always need a return value
Roughly how many array methods are there according to the MDN Web docs?
around 50
What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?
mdn
Give 6 examples of comparison operators.
== , === . > , < , <= , >=, !=
What data type do comparison expressions evaluate to?
boolean
What is the purpose of an if statement?
executes code only on specified conditions
Is else required in order to use an if statement?
it is not
Describe the syntax (structure) of an if statement.
if keyword (paranthesis) with conditions / curly brackets for code block beginning then what to return / last the closing code block }
What are the three logical operators?
&& || ! (and or not)
How do you compare two different expressions in the same condition?
with && or || (and or or operators)
What is the purpose of a loop?
to repeatedly use the same code until its condition is false / do something as fast as possible multiple times
What is the purpose of a condition expression in a loop?
so it has an end point / and stops the code or it can crash your browser
What does “iteration” mean in the context of loops?
every time it goes through a loop / is an object which defines a sequence and potentially a return value upon its termination.
When does the condition expression of a while loop get evaluated?
starts after the first run / and after each run
When does the initialization expression of a for loop get evaluated?
at the start of the loop / before it starts
When does the condition expression of a for loop get evaluated?
after the initialization expression
/ after the final expression
When does the final expression of a for loop get evaluated?
after the condition is checked / after the work as well
Besides a return statement, which exits its entire function block, which keyword exits a loop before its condition expression evaluates to false?
break keyword
What does the ++ increment operator do?
adds 1 / reassigns to value
How do you iterate through the keys of an object?
with a for… in loop
What is Array.prototype.filter useful for?
when you want to get only some items from the array back.
What is Array.prototype.map useful for?
returning a new and changing every element in the array. / lets us loop through an array and make changes and return to new array
What is Array.prototype.reduce useful for?
to reduce the array down to one value.
What is “syntax sugar”?
syntax that is designed to make code easier to read
What is the typeof an ES6 class?
Function
Describe ES6 class syntax.
keyword of class followed by the class name the {
constructor method (parameters){this.param=parameter}}What is “refactoring”?
is the process of restructuring existing computer code—changing the factoring—without changing its external behavior
What does fetch() return?
A promise
What is the default request method used by fetch()?
GET
How do you specify the request method (GET, POST, etc.) when calling fetch?
by adding a second argument to the fetch request as an object with a method property / IN ALL CAPS
