Introduction to the JavaScript strings

JavaScript strings are primitive values. Also, strings are immutable. It means that if you modify a string, you will always get a new string. The original string doesn’t change.

To create literal strings, you use either single quotes (') or double quotes (") like this:

let str = 'Hi';
let greeting = "Hello";

ES6 introduced template literals that allow you to define a string backtick (`) characters:

let name = `John`';

The template literals allow you to use the single quotes and double quotes inside a string without the need of escaping them. For example:

let message = `"I'm good". She said";

Also, you can place the variables and expressions inside a template literal. JavaScript will replace the variables with their value in the string. This is called string interpolation. For example:

let name = 'John';
let message = `Hi, I'm ${name}.`;

console.log(message);

Output:

Hi, I'm John.

In this example, JavaScript replaces the name variable with its value inside the template literal.

Escaping special characters

To escape special characters, you use the backslash \\ character. For example:

• Windows line break: '\\r\\n'
• Unix line break: '\\n'
• Tab: '\\t'
• Backslash '\\'

The following example uses the backslash character to escape the single quote character in a string:

let str = 'I\\'m a string!';

Getting the length of the string

The length property returns the length of a string:

let str = "Good Morning!";
console.log(str.length);// 13

Note: JavaScript has the String type (with the letter S in uppercase), which is the primitive wrapper type of the primitive string type. Therefore, you can access all properties and methods of the String type from a primitive string.

Accessing characters

To access the characters in a string, you use the array-like [] notation with the zero-based index. The following example returns the first character of a string with the index zero:

let str = "Hello";
console.log(str[0]);// "H"

To access the last character of the string, you use the length - 1 index:

let str = "Hello";
console.log(str[str.length -1]);// "o"

Concatenating strings via the + operator

To concatenate two or more strings, you use the + operator:

let name = 'John';
let str = 'Hello ' + name;

console.log(str);// "Hello John"

If you want to assemble a string piece by piece, you can use the += operator:

let className = 'btn';
className += ' btn-primary'
className += ' none';

console.log(className);

Output:

btn btn-primary none

Converting values to string

To convert a non-string value to a string, you use one of the following:

• String(n);
• ” + n
• n.toString()

Note that the toString() method doesn’t work for undefined and null.

When you convert a string to a boolean, you cannot convert it back. For example:

let status = false;
let str = status.toString();
// "false"
let back = Boolean(str);
// true

In this example:

• First, declare the status variable and initialize it with the value of false.
• Second, convert the status variable to a string using the toString() method.
• Third, convert the string back to a boolean value using the Boolean() function. The Boolean() function converts the string "false" to a boolean value. The result is true because "false" is a non-empty string.

Note that only string for which the Boolean() returns false, is the empty string ('');

Comparing strings

To compare two strings, you use comparison operators such as >, >=, <, <=, and == operators.

The comparison operators compare strings based on the numeric values of the characters. And it may return a string order that is different from the one used in dictionaries. For example:

let result = 'a' < 'b';
console.log(result);
// true

However:

let result = 'a' < 'B';
console.log(result);
// false

Summary

• JavaScript strings are primitive values and immutable.
• Literal strings are delimited by single quotes ('), double quotes ("), or backticks (`).
• The length property returns the length of the string.
• Use the comparison operators `>, >=, <, <=, == to compare strings.