JavaScript Strings

JavaScript Strings are immutable sequences of ordered characters, which are stored in 16 bits. If a character can’t fit in 16 bits, JavaScript use the UTF-16 encoding. As the length of the string is determinate by the number of 10-bits that compose it, if a character needs 32 bits, its length will be reported as 2. 

let euro = "€";
let smile = "😄";
console.log(euro.length);  // => 1: this character has one 16-bit element
console.log(smile.length);  // => 2

When JavaScript iterates over a string, this issue disappears 

let text = "This string has a 😄 smile";
for (let i = 0; i < text.length; ++i)
    process.stdout.write(text[i]);
process.stdout.write("\n");

for (let c of text)
    process.stdout.write(c);
process.stdout.write("\n");

Strings literals

To include a string in JavaScript, you can enclose the characters in either single quotes, double quotes, or back-ticks. 

let s1 = "This is a string";
let s2 = 'This is another string';
let s3 = `This is also a valid string`;

Operations with Strings

To create a string from different variables, we can use the + operator 

let user = "Pepe"
  let static_string = "Hello " + "World";
  let dynamic_string = "Hello, " + user

console.log(static_string);
console.log(dynamic_string);

Alternative, you can use string templates with back-ticks for a more readable approach. The string templates allows to insert break lines into the text 

let user = "Pepe";
  let age = 22;
  let msg = `Hy! I'm ${user} and I'm ${age}`;
console.log(msg);
let text1 = "This text has 2 lines\nThis is the second line";
let text2 = `This text has 2 lines
This is the second line`;

console.log(text2);
return text1 === text2;

Strings templates

let n1 = parseInt(Math.random()*10),
    n2 = parseInt(Math.random()*10);
console.log(`${n1} + ${n2} = ${n1 + n2}`);

Strings’ methods

Here are some common string methods in JavaScript: 

let myString = "This is a string";

console.log(myString.length);
console.log(myString.indexOf("is"));
console.log(myString.substring(5));
console.log(myString.substring(5, 8));
console.log(myString.at(-1)); // allows negative index
console.log(myString.charAt(0)); // does not allow negative index
console.log(myString.charCodeAt(myString.indexOf("a")));
console.log(myString.toUpperCase());
console.log(myString.toLowerCase());
console.log(myString.startsWith("This"));
console.log(myString.endsWith("This"));
console.log(myString.includes("tri"));
console.log(myString.search(/\w{5}/));
console.log(myString.replace("is", "ese").replace("is", "are"));
console.log(myString.replaceAll("is", "all"));
console.log(myString.slice(5));
console.log(myString.slice(5, 8));
console.log(myString.slice(-5));
console.log(myString.split(" "));
myString = " ".repeat(4) + myString + " ".repeat(4);
console.log(`'${myString.trim()}'`);
console.log(`'${myString.trimStart()}'`);
console.log(`'${myString.trimEnd()}'`);

References:

  • JavaScript: The definitive guide : Master the world’s most-used programming language
  • MDN Strings