JavaScript Strings

المعرفة:: JavaScript الحالة::مؤرشفة المراجع:: The Complete JavaScript Course 2022 From Zero to Expert, syahshiimi’s notes, syahshiimi’s notes, syahshiimi’s notes

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How string methods work?

Whenever we call a method on a string, JavaScript will convert that string primitive to string object with same content using new String(), that object has all string methods, and when the process is done, the object is converted back to a regular string primitive. This process is called boxing.

Getting character of a string in a specific position

const plane = "A320";
console.log(plane[0]); // A
console.log(plane[1]); // 3
console.log(plane[2]); // 2
console.log("B737"[0]); // B

String Length

const airline = "TAP Air Portugal";
console.log(airline.length); // 16
console.log("B737".length); // 4

Getting the position of a certain letter in a string

const airline = "TAP Air Portugal";
// getting the index of specific alphabet
console.log(airline.indexOf("r")); // 6 - the first position of 'r'
console.log(airline.lastIndexOf("r")); // 10 - the last position of 'r'
consoele.log(airline.indexOf("portugal")); // -1 - string wasn't found

Removing Parts of String via .slice

const airline = "TAP Air Portugal";
console.log(airline.slice(4)); // Air Portugal - starts slicing at index position 4
// Substr length = end - beginning
console.log(airline.slice(4, 7)); // Air - starts at 4 and ends at position 7

Using .slice with .indexOf to get specific strings

const airline = "TAP Air Portugal";
console.log(airline.slice(0, airline.indexOf(" "))); // TAP - extracts the first name in the string, followed by the space afterwards
console.log(airline.slice(airline.lastIndexOf(" ") + 1)); // Portugal - starts slicing from the last ' ' position + 1

Get strings from last index first - Negative slicing

const airline = "TAP Air Portugal";
console.log(airline.slice(-2)); // al
console.log(airline.slice(1, -1)); // AP Air Portugal

Change string case

const airline = "TAP Air Portugal";
 
console.log(airline.toLowerCase()); // tap air portugal
console.log(airline.toUpperCase()); // TAP AIR PORTUGAL

Fix string capitalization

const passenger = "jOnas";
const passengerLower = passenger.toLowerCase();
const passengerCorrect = passengerLower[0].toUpperCase() + passenger.slice(1);
console.log(passengerCorrect); // 'Jonas'

Trimming strings

trim() function removes trailing white space at both start and end of a string.

const s = " string with spaces ";
console.log(s.trim()); // string with spaces

String replacements

• replace:

const priceGB = '$288,07'
const priceJP = priceGB.replace('$', 'Y').replace(',' '.');
console.log(priceJP) // 288.07$

• replaceAll:

const announcement = "All passengers come to boarding door 23. Boarding door 23";
 
console.log(announcement.replaceAll("door", "gate")); // 'All passengers come to boarding gate 23. Boarding gate 23' - replaces all occurences of word "door" in the string with "gate"

• Replicating replaceAll with Regex:

console.log(announcement.replace(/door/g, "gate")); // 'All passengers come to boarding gate 23. Boarding gate 23'

String checks

Check if a word exists in a string

const plane = "Airbus A320";
console.log(plane.includes("Airbus")); // returns true
console.log(plane.includes("Boeing")); // returns false
console.log(plane.includes("Ai")); // returns true

Check if a string starts with sub-string

const plane = "Airbus A320neo";
console.log(plane.startsWith("Airb")); // true

Check if a string ends with sub-string

const plane = "Airbus A320neo";
console.log(plane.endsWith("neo")); // true
 
if (plane.startsWith("Airbus") && plane.endsWith("neo")) {
  console.log("Part of the NEW ARirbus family");
}

Split a string into an array

console.log("a+very+nice+string".split("+")); // ["a", "very", "nice", "string"]
const [firstName, lastName] = "Real Person".split(" "); // Real, Person

Combining an array into string

// using join
const newName = ["Mr.", firstName, lastName.toUpperCase()].join(" ");
console.log(newName);

Padding a string

In situations where the string needs to be a specified character length, we can use padding methods padStart and padEnd.

const message = "Go to Gate 23";
console.log(message.padStart(25, "+").padEnd(35, "+"));

Convert a number to a string

const str = 9 + ""; // '9'

String Repetition

"5".repeat(4); // 5555