Template Literals & String interpolation in JavaScript

Template literals (or Template strings) in JavaScript are multi-line string literals that allow string interpolation. String interpolation allows us to include embedded expressions as part of the string. You can create multi-line strings, basic string formatting & tagged templates with Template strings. They are part of the ES2016/ES6 specification. Template strings are also called template literals. In this tutorial, we will learn about Template strings (or Literal) how to use it in Multiline Strings & string interpolation. We will also learn how to nest expressions and how to escape template literals using the backslash (\)

What is Template Strings

Template literals are literals delimited with backticks ` instead of single quote or double quotes.

The following is a example of template string.

`Hello & Welcome to Tutorial on Template Strings`

What makes them powerful is you can include a embedded expression within them. We must include the expression inside a dollar sign and curly braces (${expression})

In the following example ${name} is an expression. The JavaScript evaluates it and replaces its value in the its original position.

`Hello ${name}, Welcome to tutorial on Template string`

Let us now explore the some of the use cases for the Template Strings

Multiline Strings

The following is an example of creating a multiline string. Just hit enter and continue in the next line. The \n character automatically gets inserted in the string.

Example

let sentence= `Javascript is the scripting language, 
that we use to make web pages interactive. 
It is written in plain text on the HTML page and runs in the browser`

console.log(sentence);


//**** output ****

//Javascript is the scripting language, 
//that we use to make web pages interactive. 
//It is written in plain text on the HTML page and runs in the browser

The multiline strings without template strings are created by inserting a \n newline character (LF).

let sentence= "Javascript is the scripting language,\n" +
"that we use to make web pages interactive.\n" +
"It is written in plain text on the HTML page and runs in the browser"

console.log(sentence);


//***output****


//Javascript is the scripting language,
//that we use to make web pages interactive.
//It is written in plain text on the HTML page and runs in the browser

As we said earlier, the /n (LF) character is inserted when you use the template strings. Hence the following code is true.

const str = `Line1
Line2`;
console.log(str);
console.log(str === 'Line1\nLine2');       // true

//***output***
//Line1
//Line2
//true

String Interpolation

string interpolation (expression Interpolation) is the process of evaluating a string literal containing one or more expressions. It evaluates the expression and coerces the result into a string. The result is then is replaced in the original string.

Example

In the following example, ${palyerName} is the expression. It is evaluated first and the resulting value Sachin Tendulkar is replaced at its place in the final string.

let playerName = "Sachin Tendulkar";    
console.log(`${playerName} is the greatest cricketer of all time`)



//**** Output ****
//Sachin Tendulkar is the greatest cricketer of all time

Multiple Expressions

const firstName = 'Students';
const topic ="Template Literals"

console.log(`Hello ${firstName}!
Welcome to the ${topic} tutorial`);


//*** output ****
//Hello Students!
//Welcome to the Template Literals tutorial

Using Expressions

The following example shows that you can use any expressions inside the template string. It uses the arithmetic expression ${a+b}

let a=1;
let b=2;
console.log(`The addition of ${a} + ${b} is ${a+b}`);


//***output ****
//The addition of 1 + 2 is 3

The following example uses the ternary conditional operator(?) in the template string.

let m=11;
console.log(`The m is ${(m==10) ?'ten':'not ten'}`);


//*** output ****
//The m is not ten

const MAX = 100;

function doSomeWork(x) {
  if (x > MAX) {
    throw new Error(`At most ${MAX} allowed: ${x}!`);
  }
}

doSomeWork(200)

Nesting Expressions

You can nest expressions

let x=10
let y=20
let varxy=`${x+y}`      //template string
console.log(`The addion of ${x} + ${y} is ${varxy}`);    //tempate string nested


//*** output ****
//The addion of 10 + 20 is 30

Escaping in template strings

The backslash \ is used for escaping inside template literals. It enables you to include backticks and ${ inside template literals:

console.log(`\``)     //output   `

console.log(`$`)      //output   $    this is ok

console.log(`${`)      //Error

console.log(`\${`)     //output  ${

console.log(`\$\{\}`)   //output  ${}

Tagged Templates

Another use of the Template string is in Tagged Templates. We tag a Template string to a function. This allows us to customize the parsing of the template string using the tagged function.

Reference

Template literals