Vanilla

Question 1

Difference between const, let, var and <blank>?</blank>

Question 2

How to create a shallow copy from an iterable object?

Answer 2

Array.from()

• let newArray = Array.from(someArray);*
• let newArray = Array.from(“string is iterable in JS”);*
• —-*—————————————————-

Question 3

How to check if something is an Array?

Answer 3

Array.isArray()

Array.isArray([]); //true

Array.isArray([1]); //true

Array.isArray(new Array()); //true

Array.isArray({}); //false

Array.isArray(null); //false

Array.isArray(undefined); //false

Array.isArray(100); //false

Array.isArray(‘Array’); //false

Question 4

How to concat Arrays?

Answer 4

Array.prototype.concat(Array.prototype)

note, this is a shallow copy

• var arr = [1,2];*
• var arr2 = [[1,2], [3,4]];*
• var newArr = arr.concat(arr2) // [1,2,[1,2],[3,4]]*
• The new Array is the shallow copy of the arguments so if we change the source it affects the copied object.*
• arr2[0][1] = 9; //[1,2,[1,9],[3,4]]*

Question 5

Difference between SomeType.someMethod() and SomeType.prototype.someMethod()?

Answer 5

no prototype means you call that method as a class method and pass it an object of that type.

prototype means that method can be called as an instance method from that object instance.

Question 6

Difference between for..in and for..of

Answer 6

for. .in gives the keys of an iterable (keys for an Object, index for an Array
for. .of gives the values of an iterable (nothing for an Object, elements for an Array)

Question 7

How to add element to beginning of Array?

How to remove element from beginning of Array?

How to add element to end of Array?

How to remove element from end of Array?

Answer 7

Array.prototype.unshift()

Array.prototype.shift()

Array.prototype.push()

Array.prototype.pop()

Question 8

How to concatenate all array elements?

Answer 8

Array.prototype.join([separator])

Question 9

How find index of search query in array?

Answer 9

arr.indexOf(searchElement[, fromIndex])

will return only the first it finds with this, need to write a loop to grab all

Question 10

How to filter array with a given condition

Answer 10

var newArray = arr.filter(callback(element[, index[, array]])[, thisArg])

Question 11

How to see if an Array has a value?

Answer 11

arr.includes(valueToFind[, fromIndex])

Question 12

How to see if an Array has any values that pass a certain condition?

Answer 12

arr.some(callback(element[, index[, array]])[, thisArg])

Question 13

How to see if an Array has any values that pass a certain condition?

Answer 13

arr.every(callback(element[, index[, array]])[, thisArg])

Question 14

How to return a new Array with each element modified by a function

Answer 14

var new_array = arr.map(function callback(currentValue[, index[, array]]) { // Return element for new_array }[, thisArg])

Question 15

How to sort an array?

Answer 15

arr.sort([compareFunction])

Question 16

How to modify an Array in place by adding/remove/modyfing elements with given argument?

Answer 16

var arrDeletedItems = array.splice(start[, deleteCount[, item1[, item2[, …]]]])

Question 17

How to select a portion of an array with a given start and possibly end index?

Answer 17

arr.slice([begin[, end]])

Question 18

How to create objects with constant params or values?

Answer 18

Object.seal(someObject) and Object.freeze(someObject)

seal will prevents params from being added

freeze will also prevent the values from being changable

Question 19

How to force a string to be a Number for a math operation?

Answer 19

add + in front

e.g.

let num0 = “2”

let num1 = 5

let sum = +num0 + num1

Question 20

How to do positive and negative numbers in javascript?

Answer 20

Number.POSITIVE_INFINITY

and

Number.NEGATIVE_INFINITY

Question 21

How to split an array into elements of an array

?

Answer 21

str.split([separator[, limit]])

Question 22

How to get UTF-16 code of a string character?

Answer 22

str.charCodeAt(index)

Question 23

How to see if a string ends or starts with certain chars?

Answer 23

str. startsWith(searchString[, position])
str. endsWith(searchString[, length])

Question 24

How to extract a certain section of a String?

Answer 24

str.slice(beginIndex[, endIndex])

Question 25

how to all lower case or all caps a String?

Answer 25

str. toLowerCase() str. toUpperCase()

Question 26

how to remove trailing and/or leading whtiespace from a string?

Answer 26

str. trim() str. trimEnd(); (alias: str.trimRight();) str. trimStart(); (alias: str.trimLeft();)

Question 27

how does rest oprator work in arrays?

Answer 27

let a, b, c; let arr = [1, 2, 3, 4, 5, 6, 7]; // Write code here [a, b, ...c] = arr; console.log(a); // 1 console.log(b); // 2 console.log(c); // [3, 4, 5, 6, 7]

Question 28

what is order of operations in logic gates being important, and beinga ble to assign stuff left to right with || called?

Answer 28

short circuiting

Question 29

How create an object using an existing object as a prototype? (Object inheritence)

Answer 29

Object.create(Object.prototype) This will copy the object, althought it's properties are stored in the \_\_proto\_\_property. so the new Object won't return any of the original Object properties when calling it, only when calling those properties, e.g.: let a = {name: "John", age: "30"}; let b = a; console. log(a); // =\> { name: 'John', age: '30' } console. log(b); // =\> { name: 'John', age: '30' } b. height = 180; console. log(a); // =\> { name: 'John', age: '30', height: 180 } console. log(b); // =\> { name: 'John', age: '30', height: 180 } console. log("---------------------------"); let c = {name: "John", age: "30"}; let d = Object.create(c); console. log(c); // =\> { name: 'John', age: '30' } console. log(d); // =\> {} d. height = 180; console. log(c); // =\> { name: 'John', age: '30' } console. log(d); // =\> { height: 180 } console. log(d.\_\_proto\_\_); // =\> { name: 'John', age: '30' } console. log(d.name); // =\> John console. log(d.age); // =\> 30 console. log(d.height); // =\> 180