Fundamentals 編

JSchallenger にチャレンジ - Fundamentals / Basics
JSchallenger にチャレンジ - Fundamentals / Arrays
JSchallenger にチャレンジ - Fundamentals / Objects
JSchallenger にチャレンジ - Fundamentals / Dates
JSchallenger にチャレンジ - Fundamentals / Sets

DOM 編

JSchallenger にチャレンジ - DOM / DOM selector methods
JSchallenger にチャレンジ - DOM / Events and user interactions
JSchallenger にチャレンジ - DOM / DOM manipulation
JSchallenger にチャレンジ - DOM / DOM fundamentals
JSchallenger にチャレンジ - DOM / Recursive functions

cyamy

Sum two numbers

Write a function that takes two numbers (a and b) as argument
Sum a and b
Return the result

回答

function myFunction(a, b) {
  return a + b;
}

cyamy

Comparison operators, strict equality

Write a function that takes two values, say a and b, as arguments
Return true if the two values are equal and of the same type

回答

function myFunction(a, b) {
  return a === b;
}

Get type of value

Write a function that takes a value as argument
Return the type of the value

回答

function myFunction(a) {
  return typeof(a);
}

Get nth character of string

Write a function that takes a string (a) and a number (n) as argument
Return the nth character of 'a'

回答

function myFunction(a, n) {
  return a[n-1]
}

cyamy

Remove first n characters of string

Write a function that takes a string (a) as argument
Remove the first 3 characters of a
Return the result

回答

function myFunction(a) {
   return a.slice(3);
}

Get last n characters of string

Write a function that takes a string as argument
Extract the last 3 characters from the string
Return the result

回答

function myFunction(str) {
  return str.slice(-3);
}

Get first n characters of string

Write a function that takes a string (a) as argument
Get the first 3 characters of a
Return the result

回答

function myFunction(a) {
  return a.slice(0,3);
}

Extract first half of string

Write a function that takes a string (a) as argument
Extract the first half a
Return the result

回答

function myFunction(a) {
  return a.slice(0, a.length / 2);
}

Remove last n characters of string

Write a function that takes a string (a) as argument
Remove the last 3 characters of a
Return the result

回答

function myFunction(a) {
  return a.slice(0,-3);
}

Return the percentage of a number

Write a function that takes two numbers (a and b) as argument
Return b percent of a

回答

function myFunction(a, b) {
  return b / 100 * a;
}

cyamy

Basic JavaScript math operators

Write a function that takes 6 values (a,b,c,d,e,f) as arguments
Sum a and b
Then substract by c
Then multiply by d and divide by e
Finally raise to the power of f and return the result
Tipp: mind the order

回答

function myFunction(a, b, c, d, e, f) {
  return (((a + b) - c) * d / e) ** f;
}

Check if a number is even

Write a function that takes a number as argument
If the number is even, return true
Otherwise, return false

回答

function myFunction(a) {
 return a % 2 === 0;
}

cyamy

Check if a number is a whole number

Write a function that takes a number (a) as argument
If a is a whole number (has no decimal place), return true
Otherwise, return false

回答

function myFunction(a) {
  return Number.isInteger(a);
}

Multiplication, division, and comparison operators

Write a function that takes two numbers (a and b) as arguments
If a is smaller than b, divide a by b
Otherwise, multiply both numbers
Return the resulting value

回答

function myFunction(a, b) {
  return a < b ? a / b : a * b;
}

Check whether a string contains another string and concatenate

Write a function that takes two strings (a and b) as arguments
If a contains b, append b to the beginning of a
If not, append it to the end
Return the concatenation

回答

function myFunction(a, b) {
  return a.includes(b) ? b + a : a + b;
}

Round a number to 2 decimal places

Write a function that takes a number (a) as argument
Round a to the 2nd digit after the comma
Return the rounded number

回答

function myFunction(a) {
   return parseFloat(a.toFixed(2),10);
}

Split a number into its digits

Write a function that takes a number (a) as argument
Split a into its individual digits and return them in an array
Tipp: you might want to change the type of the number for the splitting

回答

function myFunction(a) {
  return a
    .toString()
    .split('')
    .map((str) => parseInt(str, 10));
}

Clear up the chaos behind these strings

It seems like something happened to these strings
Can you figure out how to clear up the chaos?
Write a function that joins these strings together such that they form the following words:
'Javascript', 'Countryside', and 'Downtown'
You might want to apply basic JS string methods such as replace(), split(), slice() etc

回答

function myFunction(a, b) {
  const upperFirstA = 
    a.replace('%', '')
    .split('')
    .at(0)
    .toUpperCase();

  const validateA = 
    upperFirstA + 
    a.replace('%', '')
    .slice(1);

  const validateB = 
    b.replace('%', '')
    .split('')
    .reverse()
    .join('');

  return validateA + validateB;
}

Return the next higher prime number

This challenge is a little bit more complex
Write a function that takes a number (a) as argument
If a is prime, return a
If not, return the next higher prime number

回答

function myFunction(a) {
  const isPrime = (n) => {
    if (n === 2) return true;
    for (let i=2; i<n; i++) {
      if (n % i === 0) return false;
    }
    return true;
  }
  while(!isPrime(a)) a++;
  return a;
}

解説

素数の判定にあたっては「エラトステネスの篩」というアルゴリズムを用います。聞いたことのない方は是非調べてみてください。

cyamy

Find next higher natural number that is divisble by y

Write a function that takes two numbers, say x and y, as arguments
Check if x is divisible by y
If yes, return x
If not, return the next higher natural number that is divisible by y

回答

function myFunction(x, y) {
  while (x % y !== 0) x++
  return x
}

cyamy

Insert character after every n characters (backwards)

Write a function that takes two strings (a and b) as arguments
Beginning at the end of 'a', insert 'b' after every 3rd character of 'a'
Return the resulting string

function myFunction(a, b) {
  return Array.from(a)
    .reverse()
    .reduce((acc, cur, i) =>
      i % 3 === 0
        ? cur + b + acc
        : cur  + acc,
    );
}

Find the correct word by incrementing letters in alphabet

Write a function that takes a string as argument
As it is, the string has no meaning
Increment each letter to the next letter in the alphabet
Return the correct word

回答

function myFunction(str) {
  const [...alphabet] = 'abcdefghijklmnopqrstuvwxyz';
  const [...splitStr] = str;
  const getNextStr = (current) =>
    current === 'z'
      ? 'a'
      : alphabet[alphabet.indexOf(current) + 1];

  return splitStr
    .map((current) => getNextStr(current))
    .join('');
}

Find the position of one string in another

Write a function that takes a string as argument
The string contains the substring 'is'
Return the index of 'is'

回答

function myFunction(a) {
    return a.indexOf('is');
}

Fundamentals 編

DOM 編

Sum two numbers

回答

Comparison operators, strict equality

回答

関連内容

Get type of value

回答

関連内容

Get nth character of string

回答

Remove first n characters of string

回答

関連項目

Get last n characters of string

回答

関連項目

Get first n characters of string

回答

関連項目

Extract first half of string

回答

関連項目

Remove last n characters of string

回答

関連項目

Return the percentage of a number

回答

Basic JavaScript math operators

回答

関連項目

Check if a number is even

回答

Check if a number is a whole number

回答

関連項目

Multiplication, division, and comparison operators

回答

関連項目

Check whether a string contains another string and concatenate

回答

関連項目

Round a number to 2 decimal places

回答

関連項目

Split a number into its digits

回答

関連項目

Clear up the chaos behind these strings

回答

関連項目

Return the next higher prime number

回答

解説

Find next higher natural number that is divisble by y

回答

Insert character after every n characters (backwards)

関連項目

Find the correct word by incrementing letters in alphabet

回答

関連項目

Find the position of one string in another

回答