Array Obj properties and methods

Question 1

what do the methods arr.push() and arr.unshift do? explain the syntax and parameters

Answer 1

They add things to the end or beginning of an array respectively

Question 2

what do the methods arrVar.pop() and arrVar.shift() do? explain the syntax and parameters

Answer 2

used to remove elements to end or front of array.

Question 3

What does the method arrVar.fill() do?explain the syntax and parameters

Answer 3

fill an array with a given value, can include a range

Question 4

What does the method arrVar.reverse()? explain the syntax and parametersdo?

Answer 4

used to reverse the order of an array.

Question 5

What does the method arrVar.sort() do? explain the syntax and parameters what is the default sort order?

Answer 5

used to sort arrays in place. insert (a,b)=>a-b for acc order. remember if it starts with a it’s accending.

Question 6

How do we implement destructing, give an example with proper syntax

Answer 6

let [a, b, …rest] = [10, 20, 30, 40, 50];

console.log(rest); // expected output: [30,40,50]

Question 7

What does the method arrVar.slice() do? Give an alternative way for the same effect, also what is the parameter syntax

Answer 7

use arr.slice() or […arrVar] used to copy an existing array.

Slice’s syntax is arr.slice(begin index for slice,endindex for slice(excluded);

We can use negative numbers in slice to start from the back of an array and just copy the last item arr.slice(-1) if ther eis only one parameter passed this will return from the passed index to the end of the array.

Question 8

What does the method arrVar.indexof() of arrVar.lastIndexOf() do? What are the parameters taken.

Answer 8

used to return the first/last index of an value in an array or returns -1. takes a second option parameter for the index of where to start the search (included).

Question 9

What does the method arrVar.includes() do?explain the syntax and parameters

Answer 9

used to check an array (or string) to see if ti includes a certain value. returns true or false.

Question 10

What does the method arrVar.join() do?explain the syntax and parameters

Answer 10

used to join elements of an array… can also use arr.concat(arr2) or we can use the spread operator return […arr,…arr2] arrVar.toString() can be used to return it as well.

Question 11

What does the method arrVar.splice() do? explain the syntax and parameters

Answer 11

Adds and/or removes element(s) from an array.

arr.splice(beginIndex,HowmanyToDelete,)

Question 12

What are the properties of an array object? explain the syntax and what it does.

Answer 12

used to check the length of an array.

Question 13

What does the method arrVar.every() do? explain the syntax and parameters

Answer 13

used to check every element in array against a statement, returns true if all pass, otherwise returns false.

arrVar.every((x)=>x>3)

Question 14

What does the method arr.some() do? explain the syntax and parameters

Answer 14

used to potentially check every element in array against a statement, returns true if one passes, otherwise returns false.

arr.some((x)=>x>3)

Question 15

What does the method arrVar.filter() do? explain the syntax and parameters

Answer 15

used to create a new array with all elements that pass the test. ex. all num above 10 & all str that pass /^\w/ regex.test.

arrVar.filter((x)=>x>3)

Question 16

What does the method arrVar.find() do? explain the syntax and parameters

Answer 16

used to find the first element of an array that passes the statement. returns element .

arrVar.find((x)=>x>3)

Question 17

What does the method arrVar.forEach() do? explain the syntax and parameters

Answer 17

used to iterate through an array and execute a command (callback) but not the map one.

Question 18

What does the method arrVar.map() do? explain the syntax and parameters

Answer 18

used to iterate through each value in an array and execute a callback… can mutate the array. arrVar.map((x,i)=>x*2)

Question 19

What does the method arrVar.reduce() & arr.reduceRight() do? explain the syntax and parameters

Answer 19

used to apply function (usually a math using an accumulator and a current value to reduce the array to a single value.

arrVar.reduce((a,b)=>a+b,0);

Question 20

What are the properties of an array object? explain the syntax and what it does.

Answer 20

used to check the length of an array.

arr.length;

Question 21

What does the method arrVar.findIndex() do? Explain the syntax

Answer 21

used to find the first element of an array that passes the statement. returns element index.

arrVar.findIndex((x)=>x>3)

Question 22

How can we make an array from an a array like? What types do those include and what is the styntax? also

Answer 22

The method is .from called on the Array object, it also can take a callback which mutates each element of the array.

console.log(Array.from([1, 2, 3], x => x + x));

Question 23

What does the toString method do on an array?

Answer 23

The toString() method returns a string representing the specified array and its elements.

console.log(array1.toString());
// expected output: "1,2,a,1a"

Question 24

What does the values method do on an array?

How can we use it and what is the syntax?

Answer 24

The values() method returns a new Array Iterator object that contains the values for each index in the array.

const array1 = ['a', 'b', 'c'];
const iterator = array1.values();

for (const value of iterator) {
console.log(value); // expected output: “a” “b” “c”
}

of iterate like

var a = ['a', 'b', 'c', 'd', 'e']; 
var iterator = a.values();

console. log(iterator.next().value); // a
console. log(iterator.next().value); // b

Question 25

How do we find the length of an array?

Answer 25

arr.length

Question 26

How do we check is a variable is an array?

Answer 26

Array.isArray(var);

Array.isArray([1,2]);

Question 27

How do we remove an object from the middle of an array?

Answer 27

use a combinations of slices or concat while exempting the index to leave out..

OR use something like the filter method with the index of the item to remove as the conditional. EX arr.filter((a,b,i)=>if(i==Math.floor(arr.length/2)))a+b:a,0

OR splice can be used to indirectly remove an item

Question 28

What are some of the easiest ways to make the .map .filter .reduce functions that more powerful?

Answer 28

Use conditionals such as && or ||, also remember that the arrow functions automatically return the statement, so for more complex functions where we want to take multiple actions use a function instead and you can list actions separately like i++; return i*2; instead of having to do it all in one line.

so for filter the syntax is arr.filter((a,b,i)=>i==0?a+b:a,0);

Question 29

What are the properties methods that we can use on both arrays and strings?

syntax, parameters and expected results?

Answer 29

includes(string)
slice(firstindex(included),lastindex(excluded))
indexOf()
lastIndexOf()
.length
.concat();

Question 30

.map() .reduce() .filter() .some() .every() .find() .splice() includes() what are they good for?

What should we use to mutate?

What should we use to remove?

What should we use to add?

test truth?

finding a certain value?

Answer 30

.map is good if we need to mutate each array, maybe combo with a filter if we want to mark array indexes to remove by replacing it with a value we can filter out after would be nice.

reduce is meant for cases where we need to sum of things in an array..

filter is good for either removing an item at a certain index or removing a multitude with correct if statements.

.some is good for just that checking if at least one returns true can make exceptions with an if statement.

every is the same but remember we can use if statements to make some exceptions so everything comes out true or false.

.find is good for finding things that past 1 or multiple conditions.

includes is like .test() for arrays is just the same good for checking if a regex includes x of an array really good to replace a long if x= y or x=z. or we can use test. for strings. maybe a while statement of while(arr.includes(‘x’)) then filter can be very powerful