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Javascript Flashcards

1
Q

Implementing a function in JavaScript and call the function

A

function greet(name) {
console.log(Hello, ${name}!);
}

// Call the function
greet(“Camila”); // Output: Hello, Camila!

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2
Q

how to console.log a value

A

console.log(Hello, ${name}!);

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3
Q

how to put default parameters

A

function greet(name = “Guest”) {
console.log(Hello, ${name}!);
}

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4
Q

how to call it with desired parameters?

A

greet(“Camila”); // Output: Hello, Camila!

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5
Q

mention 7 array methods ( do not need to explain )

A

map()
filter()
reduce()
forEach()
sort()
slice()
splice()

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6
Q

mention 4 strings methods ( do not need to explain )

A

split()
join()
substring()
slice()

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7
Q

mention 3 Object Methods

A

Object.keys()
Object.values()
Object.entries()

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8
Q

mention 5 loops

A

for Loop
while Loop
do…while Loop
for…of Loop
for…in Loop

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9
Q

steps to approach a new problem (4)

A
  1. declare a function, name it, call it
  2. send input as default params
  3. write in comment which is datatype of input/output
  4. console.log the desired return
  5. detect with data type is the input, think of avaiable methods/loops
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10
Q

diference de ! y !!

A

! (Logical NOT):

The ! operator negates a value. It first coerces the value into a boolean, and then it inverts

console.log(!0); // true (0 is falsy, so !0 is true)
console.log(!’hello’); // false (non-empty string is truthy, so !’hello’ is false)

!! (Double Logical NOT):
console.log(!!0); // false (0 is falsy, so !!0 is false)
console.log(!!’hello’); // true (non-empty string is truthy, so !!’hello’ is true)

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11
Q

diference de == y ===

A

==: Realiza comparación flexible con conversión de tipos implícita.
===: Realiza comparación estricta sin conversión de tipos, verificando tanto el valor como el tipo.

console.log(5 == ‘5’); // true (porque ‘5’ se convierte a número)
console.log(null == undefined); // true (considerados iguales en comparación débil)
console.log(0 == false); // true (0 y false son considerados iguales)

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12
Q

check if its an array

A

Array.isArray(cleanWord)

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13
Q

how to remove a space of letter with js?

A

let result = str.replace(/\s/g, ‘’); // Removes all spaces

let result = str.replace(/l/g, ‘’); // Removes all lowercase “l”

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14
Q

how to loop easy over an array?

A

arr.map((item, index) => {

    if (item === target)
    {
      indexFounded = index;
    }
})

.map() is meant for transforming arrays (i.e., creating a new array from the existing one).

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15
Q

why .map is not good idea to use it for a loop?

how to re do this? arr.map((item, index) => {

    if (item === target)
    {
      indexFounded = index;
    }
})
A

arr.forEach((item, index) => {
if (item === target) {
indexFounded = index;
}
});

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16
Q

why this is wrong? arr.length()

A

arr.length (length is a property, not a method).

17
Q

sort Method, for arrays.
give an example to order: [1, 2, 5, 5, 6, 9]

A

orderArray.sort((a, b) => a - b);

18
Q

how to order this manually?
without sort:
orderArray.sort((a, b) => a - b);

4 steps

A

we need a nested loop.

  1. we need a forEach item
    arr.forEach(item => {

for each item in the array we need to see where to add it.

  1. for (let i = 0; i < orderArray.length; i++) {
    }
  2. inside the secound loop:

if (item < orderArray[i]) {
orderArray.splice(i, 0, item); // Insert at index i
inserted = true;
break;
}

if it dosent get in here then, we put it in the last place.

  1. if (!inserted) {
    orderArray.push(item);
    }
19
Q

what method can i use for:
1.array
2.modify add, remove into an existing one

A

splice method is used to add, remove, or replace elements in an array. It modifies the original array in place and returns an array containing the removed elements

20
Q

how to use splice just to add an item and avoid deleting.

A

splice(i, 0, item) Works Here
i:
This is the index where the item will be inserted in the orderArray.

0:
The deleteCount is 0, meaning no elements in the orderArray are removed. The array will just expand to accommodate the new item.

item:
This is the element being added to the orderArray.

21
Q

why the function sortNamesByLength () was inserting double in the new array

function sortNamesByLength(arrNames = [“Alice”, “Bob”, “Charlie”, “David”]) {
//input is an array
//output new arrau sorred
let sortedPerLenght = [];

//add into new array
// if its smaller than other, then add it in the index of that. inserted it

arrNames.forEach((item) => {
let inserted = false;

for (let i = 0; i < sortedPerLenght.length; i++) {
  if (item.length < sortedPerLenght[i].length) {
    console.log(sortedPerLenght[i])
    console.log(sortedPerLenght[i].length)
    sortedPerLenght.splice(i, 0, item);
    break;
  }
}

if (!inserted) {
    sortedPerLenght.push(item);
}   });

return sortedPerLenght;
}

console.log(sortNamesByLength());

A

You need to update inserted to true once the item is successfully inserted using splice().

22
Q

in why the function sortNamesByLength () why a break is needed in:

for (let i = 0; i < sortedPerLenght.length; i++) {
if (item.length < sortedPerLenght[i].length) {
console.log(sortedPerLenght[i])
console.log(sortedPerLenght[i].length)
sortedPerLenght.splice(i, 0, item);
break;
}
}

A

Imagine an array sortedPerLenght = [3, 5, 8] and you want to insert 4. After comparing with 3:

You insert 4 between 3 and 5.
Continuing to check 4 against 5 or 8 doesn’t make sense because the array is already sorted, and 4 will always be smaller than 5 and 8.

23
Q

what is the issue here: with index

arr.forEach((item, index) => {

    for (let i=index; i < arr.length ; i++){
        if (item + arr[i] === target )
        {
            uniquePairsArray.push([item, arr[i]]);
            break;
        }
    }
}
)
console.log(uniquePairsArray);
debugger
return uniquePairsArray;
A

Inner loop: Starts from index + 1 to avoid pairing the element with itself.

The inner loop should not start at the same index as the outer loop, as that would lead to pairing a number with itself. Instead, you should ensure that the inner loop starts from the next index to avoid duplicates like [item, item].

24
Q

in interview how to test 3 times your function…

A

we need 3 console.log and 3 params

25
Q

why is not entering in the loop?

function findMaxInArr (arr= [1, 3, 7, 2]) {
let maxValue = null;

console.log(arr.length)
for (let i; i < arr.length; i++) {
    if (arr[i] > maxValue || maxValue == null){
        maxValue= arr[i]
    }
}

return maxValue; }

console.log(findMaxInArr());

A

The issue is that the variable i in your for loop is not initialized. In JavaScript, the syntax for a for loop requires initializing the loop variable.

26
Q

why the secound index is wrong?

arr.forEach((item, index) => {
for (let i = index; i < arr.length; i++) {
console.log(item + arr[i] === target);
if (item + arr[i] === target) {
sumedNum = [item, arr[i]];
break;
}
}
});
return sumedNum;

A

Start Inner Loop at index + 1:

To avoid adding the same element to itself, the inner for loop starts at index + 1.

27
Q

how to check if the num is divisible in js. with / or %.

A

num % 3 === 0 && num % 5 === 0.

The modulus operator gives the remainder of a division.

28
Q

menor/igual en js

A

console.log(a <= b);

29
Q

how to create a copy of two arreys into one!!! camila!

A

let oneSortedArray = […arr1, …arr2]

30
Q

what to do if i want to map over and array and also modify it?

A

use a for! for (let index = 0; index < oneSortedArray.length; index++) {

DO NOT map over the array or FOREACH over it

31
Q

como acceder a la 3er letra de un string usando un for

A

for (let i = 0; i < str.length ; i++){
newWord= str[i]+ newWord;
}

32
Q

como chequear si hay una letra en un string? ejemplo letra a..
hay un metodo..

A

if (currentSub.includes(char)) {
currentSub = currentSub.slice(currentSub.indexOf(char) + 1);
}

33
Q

can i use foreach with a string?

A

Strings don’t have a .forEach
you can use split(“”) to convert the string into an array of characters.

34
Q

explica esto con palabras:
numList.forEach((num) => {
let inserted = false;

for (let i = 0; i < orderList.length; i++) {
  // Check if num should be inserted before orderList[i]
  if (num < orderList[i]) {
    // Insert num in the correct position
    orderList.splice(i, 0, num);
    inserted = true;
    break;
  }
}

// If num is greater than all elements, push it at the end
if (!inserted) {
  orderList.push(num);
}   });
A
35
Q

can i put a break in a forEach?

A

one key difference between forEach and a traditional for loop is that you cannot use the break statement inside forEach

const arr = [1, 2, 3, 4, 5];

for (const num of arr) {
if (num === 3) {
break; // Breaks out of the loop
}
console.log(num);
}

36
Q

what to use when mapping an array and using break (2 options)

A

for (const num of arr) {
if (num === 3) {
break; // Breaks out of the loop
}
console.log(num);
}

for (let i = 0; i < nums2.length; i++) {
  if (nums2[i] === item1) {
    duplicated = item1;
    break;
  }
}
37
Q

by using a stack. A stack is a data structure that follows the Last In, First Out (LIFO) principle

A

function isValid(s) {
// Stack to keep track of opening parentheses
let stack = [];

// Mapping of closing parentheses to opening parentheses
const map = {
‘)’: ‘(‘,
‘}’: ‘{‘,
‘]’: ‘[’
};

// Traverse each character in the string
for (let char of s) {
// If the character is a closing parenthesis
if (map[char]) {
// Pop the top of the stack, or set to a dummy value if the stack is empty
let topElement = stack.length === 0 ? ‘#’ : stack.pop();

  // Check if the top element matches the corresponding opening parenthesis
  if (topElement !== map[char]) {
    return false;
  }
} else {
  // If it's an opening parenthesis, push it to the stack
  stack.push(char);
}   }

// If the stack is empty, all parentheses were matched correctly
return stack.length === 0;
}

// Test cases
console.log(isValid(“()”)); // true
console.log(isValid(“()[]{}”)); // true
console.log(isValid(“(]”)); // false
console.log(isValid(“([)]”)); // false
console.log(isValid(“{[]}”)); // true

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