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Strings

Strings are text in quotation marks - single quotes (' ') double quotes (" "), or backtick quotes.

See the example below:

const str1 = 'This is a text in the single quote.';
const str2 = "This is a text in double-quotes.";
const str3 = `This is a text in backticks quotes.`;

Strings also includes pretty nice methods like includes('...'), indexOf('...'), etc.

const str = 'This is a text in the single quote.';

str.includes('text'); // true

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The internal format for strings is always UTF-16

String Template Literals

Backticks are best used for template literals.

The syntax for the template literals is shown below:

`... ${expression} ...`

See the example below:

const myName = (fName, lName) => {
    return fName + ' ' + lName;
};

console.log(`His name is ${myName('Osagie', 'Bello').}`);
// His name is Osagie Bello.

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String in Multi-lines

Text in backtick can easily span multiple lines.

See the example below:

const str = `Hello World! 
My name is: 
Last Name - Bello
FirstName - Osagie`;

console.log(str);

/*
Hello World! 
My name is: 
Last Name - Bello
FirstName - Osagie
*/

Alternatively, the newline character \n can be used to escape to a new line.

See the example below:

const str = 'Hello World!\nMy name is:\nLast Name - Bello\nFirstName - Osagie';

console.log(str);

/*
Hello World!
My name is:
Last Name - Bello
FirstName - Osagie
*/

Instead of having all text in a single line, you can escape to a new line with the \.

See the example below:

const str = 'Hello World!\n\
My name is:\n\
Last Name - Bello\n\
FirstName - Osagie';

console.log(str);

Quotes in String

It is possible to insert quotes in a string.

See the example below:

const str1 = 'Martin Luther King once said "The time is always right to do what is right". 🤔';
const str2 = "Martin Luther King once said \"The time is always right to do what is right\". 🤔";
const str3 = `Martin Luther King once said "The time is always right to do what is right". 🤔`;
const str4 = 'It\'s my birthday. 😁';
const str5 = `It's my birthday. 😁`;

Only the quotes that are the same as the enclosing ones need to be escaped.

MDN contains the complete list of escape characters.

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String Length

The string length is the number of characters in a word or sentence (including space).

The syntax is:

str.length

See the example below:

'Hello World'.length; // 11
'Hello\nWorld'.length; // 11

Escape characters, spaces are all special characters included in the .length count.

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Accessing Characters

The zero-based index is used to access characters in a string.

str[numPos]

The numPos is in a zero-based index position.

See the example below:

const str = `Hello World`;

// the first character
console.log( str[0] ); // H

// the fifth character
console.log( str[4] ); // o

Alternatively, the charAt(...) method can be used

str.charAt(numPos)

See the example below:

const str = `Hello World`;

// the first character
console.log( str.charAt(0) ); // H

// the fifth character
console.log( str.charAt(4) ); // o

The easy way to access characters counting from the last index is to use the length number property.

str[str.length-N] // N = 1, 2,...
str.charAt(str.length-N) // N = 1, 2,...

See the example below:

const str = `Hello World`;

console.log( str.charAt(str.length-1) ); // d
console.log( str[str.length-1] ); // d

The above example is the same as below:

console.log( str.slice(-1) ); // d

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Looping String characters

Iteration can be performed on string characters using for..of

for (let char of "Hello") {
  console.log(char);

  /* 
  H
  e
  l
  l
  o => char is now o
  */

  char === 'H' // false
  char === 'e' // false
  char === 'l' // false
  char === 'o' // true
},

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Immutable Strings

Once a string is created, it can't be changed

const myName = 'Bello';

myName[2] = 'y';
console.log( myName, myName[2] ); // Bello l

You can use the replace method replace(...) to replace part a string.

The syntax is shown below:

str.replace(oldStr, newStr)

See the examples below:

const myName = 'Bello';

const newName = myName.replace('Bello', 'Beylo');
console.log( newName, newName[2] ); // Beylo y

const str = "I love front-end web development"
const newStr = str.replace('front', 'back');
console.log(newStr); // I love back-end web development

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String Methods

There are a couple of ways to use a method on a string.

See the example below of some built-in method:

let str = 'Bello';
console.log( str.toUpperCase() ); // BELLO
console.log( str.toLowerCase() ); // bello

str = 'bello';
console.log( str[0].toUpperCase(), str ); // B bello

str = 'Hello Bello';
console.log( str.startsWith("Hel") ); // true
console.log( str.endsWith("ello") ); // true
console.log( str.endsWith("Bell") ); // false

str = '#DevCommunity';
console.log( str.startsWith("#Dev") ); // true
console.log( str.endsWith("unity") ); // true

str = 'JavaScript is one of the best programming languages';
console.log( str.indexOf('Script') ); // 4 => S is defined in Script
console.log( str.indexOf('script') ); // -1 => s is undefined in script

str = 'name1, name2, name3, name4,... nameN';
const name = 'name';
console.log(`The index of the first "${name}" 
from the end of the string is ${str.lastIndexOf(name)}`);

/*
The index of the first "name" 
from the end of the string is 31
*/

console.log(`The index of the first "${name}" 
from the start of the string is ${str.indexOf(name)}`);

/*
The index of the first "name" 
from the start of the string is 0
*/

str.includes('name3'); // true

const row = 'row, ';
const boat = 'boat...';
str = `${row.repeat(3)}the ${boat.repeat(1)}🎶`; 
console.log(str); // row, row, row, the boat...🎶

str = 'Longest word: pneumonoultramicroscopicsilicovolcanoconiosis'
console.log( str.slice(0, 20) ); 
// Longest word: pneumo => 0 to 19, 20 not included

str = 'Bello Osagie';
console.log( str.slice(6) ); 
// Osagie => same as (str.slice(6, str.length) )

str = "stringify";
console.log( str.slice(-4, -1) ) // gif

console.log( str.substring(2, 6) ) // ring
console.log( str.slice(2, 6) ) // ring
console.log( str.slice(2, 6) ) // ring
console.log( str.substr(2, 4) ); // ring
str.substr(-4, 2); // gi

console.log( str.substring(2, 6) === str.substring(6, 2) ) // true
console.log( str.slice(2, 6) === str.slice(6, 2) ) // false

const greeting = '   Hello world!   ';

console.log(greeting.trim()); // Hello world!;

str = '6';

console.log(str.padStart(2, '0')); // 06
console.log(str.padStart(3, '0')); // 006
console.log(str.padStart(3, '1')); // 116

const accountNum = '168939002125581';
const last4Digits = accountNum.slice(-4);
const encrypt = last4Digits.padStart(accountNum.length, '*');
console.log(encrypt); // ************5581

console.log( `confirm your account number: ${encrypt}` );
// confirm your account number: ************5581

MDN contains the complete list of string methods.

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Iterable Strings

A String is iterable because it is a collection of characters. It iterates over each character in a string.

See the example below:

const myString = 'Bello Osagie';

for (let char = 1; char <= myString.length-1; char++) {
  console.log(myString[char]);
}

/*
B
e
l
l
o

O
s
a
g
i
e
*/

An alternative approach is to use for...in.

The example above is the same as below:

const myString = 'Bello Osagie';

for (let char in myString) {
  console.log(myString[char]);
}

We can also use for...of to loop through each character in a string.

const myString = 'Bello Osagie';

for (let char of myString) {
  console.log(char);
}

The for...of is faster than for...in when iterating only characters.

Happy coding!!!

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