JavaScript の基礎: パート 2

const name = "John Doe";
const dateOfBirth = "2000-12-25";
const profession = "Software Engineer";
const numberOfPets = 2;
const weightOfProteinInGrams = 12.5;
const hasAJob = true;

const sentence = `Full name: ${name}, date of birth: ${dateOfBirth}, profession: ${profession}`;
console.log(sentence);

const name = "John Doe";
const dateOfBirth = "2000-12-25";
const profession = "Software Engineer";
const numberOfPets = 2;
const weightOfProteinInGrams = 12.5;
const hasAJob = true;

const sentence =
  "Full name: " +
  name +
  ", date of birth: " +
  dateOfBirth +
  ", profession: " +
  profession;

console.log(sentence);

const someName = "Doe";

const firstChar = someName[0];
const secondChar = someName[1];
const thirdChar = someName[2];

console.log(
  `The characters in "${someName}" are: '${firstChar}', '${secondChar}' and '${thirdChar}'`
);
// The characters in "Doe" are: 'D', 'o' and 'e'

// Using string methods and properties
const fullName = "John Doe";

// NB: whatever method we can call on a string literal,
//we can do the same for a variable

// find and print out the length of the fullName string
// variable using the length property
const fullNameLength = fullName.length;

// using string interpolations here
console.log(`The name, "${fullName}", has ${fullNameLength} characters`);

// counting includes the spaces and symbols too
// update the value of fullName and see what happens

// this is the same as above but I will encourage you
// to stick to string interpolations in cases like this
// console.log("The name, " + fullName + ", has " + fullNameLength + " characters");

// convert uppercase and lowercase
console.log(`Upper: ${fullName.toUpperCase()}`);
console.log(`Lower: ${fullName.toLowerCase()}`);

// check if fullName starts with John
const startsWithKey = "John";
const fullNameStartsWithJohn = fullName.startsWith(startsWithKey);
console.log(
  `It is ${fullNameStartsWithJohn} that "${fullName}" starts with "${startsWithKey}"`
);

const endsWithKey = "Doe";
const fullNameEndsWithDoe = fullName.endsWith(endsWithKey);
console.log(
  `It is ${fullNameEndsWithDoe} that "${fullName}" ends with "${endsWithKey}"`
);

// try this yourself, check if fullName starts with john and doe,
// then uppercase and lowercase the key and try again (for both cases)

// check if fullName as a space
const fullNameHasASpace = fullName.includes(" ");
// here we passed the key/search string directly without creating a variable.
// I want you to know that we can also do that
console.log(`It is ${fullNameHasASpace} that "${fullName}" has a space`);
// we could have also done
// console.log(`It is ${fullName.includes(" ")} that "${fullName}" has a space`);

// try checking if the fullName contains the letter J, either uppercase or lowercase
// how would you achieve this? refer to the methods above for clues, first

// replace Doe with Moe
const moedFullName = fullName.replace("Doe", "Moe");
console.log(`New full name: ${moedFullName}`);

// try replacing spaces with underscore
const stringWithStaringAndTrailingSpaces = " John Doe ";
console.log(
  stringWithStaringAndTrailingSpaces
    .replace(" ", "JS") // replaces the first " "
    .replace(" ", "_") // replaces the second " "
    .replace(" ", "TS") // replaces the third " "
);

// it replaces only one instance at a time. so it was chained.
// I don't have to create a temp variable

// trust me, having your users start their email with spaces is annoying
// and sometimes it's the input keyboard (I get it, I am just venting off)
// but then again it will not harm trimming the unnecessary (white) spaces
// we will trim the whites off the stringWithStaringAndTrailingSpaces
// we'd use another method to let you know that the trimming worked
console.log(
  `Length of original string: ${stringWithStaringAndTrailingSpaces.length}`
);

console.log(
  `Length of trimmed string: ${
    stringWithStaringAndTrailingSpaces.trim().length
  }`
);
// remember the definition of the length, it counts the spaces too

// split is really useful, we can split the full name into the first
// and last name in order as is
// i don't think it will be pretty to have spaces with the names
// we'd do the splitting at the space
console.log(stringWithStaringAndTrailingSpaces.split(" "));
console.log(stringWithStaringAndTrailingSpaces.trim().split(" "));
// printing the split string (becomes an array) shows the content
// of the array (or string to be precise)
// note any difference? Would the assumption still hold that the
// first element (object) in the array will be the first name and
// second (which should be the last actually) is the last name?
// this doesn't hold anymore because of the starting and trailing spaces

// substring(starting [, ending])
const someLongString = "This is some long string";
const substringFromTwoToEight = someLongString.substring(2, 8);
console.log(substringFromTwoToEight);
// is is

const substringFromStartToTwelve = someLongString.substring(0, 12);
console.log(substringFromStartToTwelve);
// This is some

const substringFromTenth = someLongString.substring(10);
console.log(substringFromTenth);
// me long string

// chartAt and indexOf
const veryWeakPassword = "qwerty12";

const indexOfTee = veryWeakPassword.indexOf("t");
console.log(`The first 't' in "${veryWeakPassword}" is at index ${indexOfTee}`);
// The first 't' in "qwerty12" is at index 4

// Note that there is no 'v'
const indexOfVee = veryWeakPassword.indexOf("v");
console.log(`The first 'v' in "${veryWeakPassword}" is at index ${indexOfVee}`);
// The first 'v' in "qwerty12" is at index -1

// based on the result of the above (using the indexOf Tee which was 4)
// let's find the value at index 4
const characterAtIndexFour = veryWeakPassword.charAt(4);
// we could have passed 'indexOfTee'
console.log(`The character at index '4' is '${characterAtIndexFour}'`);
// The character at index '4' is 't'

const characterAtIndexNegativeOne = veryWeakPassword.charAt(-1);
console.log(`The character at index '4' is '${characterAtIndexNegativeOne}'`);
// returns an empty string
// The character at index '4' is ''

// password_verification.js
const veryWeakPassword = "qwerty12";
console.log(`Password validation for "${veryWeakPassword}"`);

// - be six characters
const passwordLength = veryWeakPassword.length;
console.log(
  `- Password must have 6 characters => "${veryWeakPassword}" has '${passwordLength}' characters`
);
// so it is a valid password based on our rules?

// - start with uppercase p, 'P'
const startsWithPee = veryWeakPassword.startsWith("P");
console.log(
  `- Password must start with 'P' => it is ${startsWithPee} that "${veryWeakPassword}" starts with 'P'`
);

// we can also check the first character, index 0.
const firstCharacter = veryWeakPassword[0];
console.log(
  `- Password must start with 'P' => "${veryWeakPassword}" starts with '${firstCharacter}'`
);

// - end with underscore
const endsWithUnderscore = veryWeakPassword.endsWith("_");
console.log(
  `- Password must end with '_' => it is ${endsWithUnderscore} that "${veryWeakPassword}" ends with '_'`
);

// from the index concept, the last character will be at index, length of string minus one
const lastCharacter = veryWeakPassword[veryWeakPassword.length - 1];
console.log(
  `- Password must start with 'P' => "${veryWeakPassword}" ends with '${lastCharacter}'`
);

// - have uppercase q, 'Q'
const hasUppercaseQue = veryWeakPassword.includes("Q");
console.log(
  `- Password must have uppercase q, 'Q' => it is ${hasUppercaseQue} that "${veryWeakPassword}" has 'Q'`
);

// we can use the index approach
const indexOfUppercaseQue = veryWeakPassword.indexOf("Q");
console.log(
  `- Password must have uppercase q, 'Q' => 'Q' is at index '${indexOfUppercaseQue}' of "${veryWeakPassword}"`
);
// we know that index -1 means, there 'Q' was not found

// - have lowercase r, 'r'
const hasLowercaseArr = veryWeakPassword.includes("r");
console.log(
  `- Password must have lowercase r, 'r' => it is ${hasLowercaseArr} that "${veryWeakPassword}" has 'r'`
);

// we can use the index approach too
const indexOfLowercaseArr = veryWeakPassword.indexOf("r");
console.log(
  `- Password must have lowercase r, 'r' => 'r' is at index '${indexOfLowercaseArr}' of "${veryWeakPassword}"`
);
// we know that index -1 means, there 'r' was not found

// - have its fifth character as uppercase v, 'V'
// fifth character with have index = fifth position - 1 = 4
// const fifthCharacter = veryWeakPassword[4]
const fifthCharacter = veryWeakPassword.charAt(4);
console.log(
  `- Password must have its fifth character as uppercase v, 'V' => "${veryWeakPassword}" has its 5th character as '${fifthCharacter}'`
);

// using the index approach, 'V' must have an index of 4 (same index logic as above)
const indexOfVee = veryWeakPassword.indexOf("V");
console.log(
  `- Password must have its fifth character as uppercase v, 'V' => 'V' is at index '${indexOfVee}' of "${veryWeakPassword}"`
);

Password validation for "qwerty12"
- Password must have 6 characters => "qwerty12" has '8' characters
- Password must start with 'P' => it is false that "qwerty12" starts with 'P'
- Password must start with 'P' => "qwerty12" starts with 'q'
- Password must end with '_' => it is false that "qwerty12" ends with '_'
- Password must start with 'P' => "qwerty12" ends with '2'
- Password must have uppercase q, 'Q' => it is false that "qwerty12" has 'Q'
- Password must have uppercase q, 'Q' => 'Q' is at index '-1' of "qwerty12"
- Password must have lowercase r, 'r' => it is true that "qwerty12" has 'r'
- Password must have lowercase r, 'r' => 'r' is at index '3' of "qwerty12"
- Password must have its fifth character as uppercase v, 'V' => "qwerty12" has its 5th character as 't'
- Password must have its fifth character as uppercase v, 'V' => 'V' is at index '-1' of "qwerty12"