Basic Syntax

Question 1

JS: console.log()

Answer 1

‘Print’ to screen

Question 2

JS: .length

Answer 2

Return the length of a string variable

Question 3

JS: . toUpperCase()

Answer 3

Change string to capitals

Question 4

JS: . startsWith(n)

Answer 4

Returns a Boolean depending on your input value -(n)

Question 5

JS: .trim()

Answer 5

Removes white space!
Also trimEnd or trimStart

Question 6

JS: Math.random()

Answer 6

Return a random number between 0 and <1

Question 7

JS: Math.floor()

Answer 7

Round down a decimal to nearest int

Question 8

JS: Math.ceil(Math.random() * n);

Answer 8

Round up a decimal to nearest int with random number gen

Question 9

JS: Number.isInteger()

Answer 9

Checks variable (number) and Returns a Boolean

Question 10

What are the 7 fundamental data types in JS?

Answer 10

Strings
Numbers
Booleans
Null
Undefined
Symbol
Object

Question 11

JS: let var =
const var. =

Answer 11

Use to assign a variable

Question 12

JS: let

Answer 12

Signals a variable can be reassigned a new value

Question 13

JS: const

Answer 13

Assign an immutable variable

Question 14

JS: some string with ${someVar) included ;

Answer 14

String interpolating (bit like a python f-string)

Question 15

JS: typeof
Eg. console.log(typeof myVar);

Answer 15

To return the data type of the stored value.

Question 16

JS: if (condition) {
//execute this code
} else {
// execute this code
}

Answer 16

Basic conditional

Question 17

JS: What’s the ‘and’ operator

Answer 17

&&

Question 18

JS: What’s the ‘or’ operator?

Answer 18

||

Question 19

JS: What’s the ‘not’ operator?

Answer 19

!

Question 20

JS: Give the ‘falsy’ values.

Answer 20

0 , “” , null, undefined, NaN

Question 21

JS: let VAR = VAR || ‘fresh input’

Answer 21

Short circuit evaluation

Question 22

JS: VAR ? execute code : execute code;

Answer 22

Ternary operator
Checks if VAR is true then else

Question 23

JS: const someVar = function () {
}

Answer 23

A function expression (anonymous function)

Question 24

JS: const someVar = () => {
}

Answer 24

An arrow function

Question 25

JS: const = someVar = param => num * num;

Answer 25

Concise body function
() removed from someVar
{} removed since only a single line function
Return is implicit
Would otherwise like like
const someVar = (num) => {
return num * num;
};

Question 26

JS: STRING[n];

Answer 26

Access an index of a string

Question 27

JS: STRING.slice(indexinc, indexex);

Answer 27

Get a slice (range of characters) from a string.
NB: lower index is inclusive, upper is exclusive

Question 28

JS: array.push(INPUT);

Answer 28

Add an element to the end of an array
Returns the new length

Question 29

JS: array.unshift(INPUT);

Answer 29

Adds an element to the start of an array.

Question 30

JS: array.pop();

Answer 30

Remove the last element from an array. Method returns the removed value.

Question 31

JS: array.shift()

Answer 31

Removes first element (value not index) from an array return the value

Question 32

JS: new array = array1.concat(array2);

Answer 32

Combine 2 arrays to create new (and leaving the old ones unchanged

Question 33

JS: array .indexOf(INPUT);

Answer 33

find the index location of the input value

Question 34

JS: array.join();

Answer 34

Turn the array into a string. You can input your own separator choice as an argument: e.g .join(“, “)

Question 35

JS: array.includes(INPUT)

Answer 35

returns true or false

Question 36

JS: array. revers();

Answer 36

Modifies the original! Otherwise self explanatory

Question 37

JS: array.sort((a, b) => a -b);

Answer 37

modifies the original sort ascending or do b- a for descending

Question 38

JS: array.slice(index, index)

Answer 38

creates a new array from the slice, end index is not included)

Question 39

JS: array.splice(index, count, optionalItem);

Answer 39

Removes ‘count’ elements from array starting at ‘index’ or from 0 index if no index included.
optionalItem added to the array from indeed

Question 40

JS: obj[‘key n’];
Or obj.keyn (if valid identifier)

Answer 40

Retrieve a value from an object but its key

Question 41

JS: object[‘key’] = value;
Or. object.key = value;

Answer 41

Add or replace a key-value pair

Question 42

JS: Object. keys(OBJECT);

Answer 42

Returns the keys of the object as an array

Question 43

JS: Object.entries(OBJECT);

Answer 43

returns a 2d array of key-value pairs

Question 44

JS: JSON.stringify(nestedObject);

Answer 44

Returns a JSON represented string of nested object

Question 45

JS: setTimeout(yourArg, msdelay)

Answer 45

Delay function. Second argument is delay in milliseconds.i.e 1000 for 1 second

Question 46

JS: passing a function as an argument?

Answer 46

Don’t use ()

Question 47

JS: ARRAY.find(item => itemCRITERA);

Answer 47

Find the first element in a array that matches criteria

Question 48

JS: ARRAY.filter(item => itemCRITERA);

Answer 48

Returns a new array with elements that pass the test implemented by the function

Question 49

JS: ARRAY.map( ITEM => function content);

Answer 49

Returns a new array with the results of function on every element

Question 50

JS: Math.hypot(dx, dy);

Answer 50

Find the hypotenuse; straight line distance between points x and y

Question 51

JS: array.indexOf(“element”)(

Answer 51

Returns the index num of the element

Question 52

JS. array.splice (start index, num of indices, replacement)

Answer 52

Swap out part of an array

Question 53

JS: array.reduce((acc, curr) => acc + curr, 0)

Answer 53

Executes a reducer function on each element resulting in single value output

Question 54

array.forEach(item => function)

Answer 54

Execute function on each item

Question 55

Object.assign(target, source)

Answer 55

Copies (and overwrites if existing values) properties from source object to target, then returns the target