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#JavaScript - ${whatAre} tagged template literals?

Template literals MDN documentation
Template literals MDN documentation

On MDN, template literals are defined as string literals allowing embedded expressions. It makes composing strings with variables and multiline strings more convenient. Instead of using quotes to enclose strings, you use back-ticks ` ` to encase template literals. 

Template Literals

For examples: 
Without template string
let transitionDuration = 1;
let transitionDelay = 2;
console.log('Transition time is ' + (transitionDuration + transitionDelay));

Using template literal

let transitionDuration = 1;
let transitionDelay = 2;
console.log(`Transition time is $(transitionDuration + transitionDelay)`);

Nesting template literals

const screenWidth = `width: ${isDesktop() ? '90' :`${(isTablet() ? '95' : '100')}` }vw`;


Template Literal Example


Tagged Template Literals

Using Tagged Template Literals, you can parse template literals with a function. The first argument of a tag function is an array consists of strings broken at embedded expressions.

For example:
The template string here is `today is ${today}`

let today = 'Tue'
console.log`today is ${today}`
["today is ", "", raw: Array(2)] "Tue" // return from console.log


let today = 'Tue'
let tomorrow = ‘Wed'
console.log`today is ${today} and tomorrow will be ${tomorrow}.`
["today is ", " and tomorrow will be ", ".", raw: Array(3)] "Tue" "Wed"

Tagged Template Literal Example

Tagged Template Literal Example


We can use the expressions in the string literals to execute a function.
For example:

var addOne = (toAdd) => { return 1 + toAdd }
addOne(1) // return 2

var addTwo = (input, toAdd) => {
    return 2 + toAdd;
}
var number = 7;
addTwo`add this ${number}` // return 9  
addTwo`add this ${number > 10 ? 5 : 2}` // return 4

Function stored in a variable

Tagged Template Literal without handling input

Tag Function with Template Literal
Tag Function with Template Literal


Because Tagged Template Literal, there is a new way called styled-components to write CSS for React and React Native components.

Note
1) It is used in graphql-tag for JavaScript applications.

Thank you for reading!

Jun