JavaScript Template Literals In Depth
Before ES6, you use single quotes (') or double quotes (") to wrap a string literal. And the strings have very limited functionality.
To enable you to solve more complex problems, ES6 template literals provide the syntax that allows you to work with strings more safely and cleanly.
In ES6, you create a template literal by wrapping your text in backticks (`) as follows:
let simple = `This is a template literal`;Code language: JavaScript (javascript)
and you get the following features:
- A multiline string: a string that can span multiple lines.
- String formatting: the ability to substitute part of the string for the values of variables or expressions. This feature is also called string interpolation.
- HTML escaping: the ability to transform a string so that it is safe to include in HTML.
The basic syntax of JavaScript template literals
As mentioned earlier, instead of using the single quotes or double quotes, a template literal uses backticks, as shown in the following example:
let str = `Template literal in ES6`;console.log(str);// Template literal in ES6
console.log(str.length); // 23
console.log(typeof str);// string
Code language: JavaScript (javascript)
Using the backticks, you can freely use the single or double quotes in the template literal without escaping.
let anotherStr = `Here's a template literal`;Code language: JavaScript (javascript)
If a string contains a backtick, you must escape it using a backslash (\) :
let strWithBacktick = `Template literals use backticks \` insead of quotes`;Code language: JavaScript (javascript)
Multiline strings
Before ES6, you use the following technique to create a multi-line string by manually including the newline character ( \n) in the string as follows:
let msg = 'Multiline \n\
string';console.log(msg);
//Multiline
//string
Code language: JavaScript (javascript)
Note that the backslash ( \) placed after the newline character ( \n) indicates the continuation of the string rather than a new line.
This technique, however, is not consistent across JavaScript engines. Therefore, it was pretty common to create a multiline string that relies on an array and string concatenation as follows:
let msg = ['This text',
'can',
'span multiple lines'].join('\n');Code language: JavaScript (javascript)
The template literals allow you to define multiline strings more easily because you need to add a new line in the string wherever you want:
let p =
`This text
can
span multiple lines`;Code language: JavaScript (javascript)
Note that the whitespace is a part of the string. Therefore, you need to ensure that the text lines up with proper indentation. Suppose you have a post object:
let post = {
title: 'JavaScript Template Literals',
excerpt: 'Introduction to JavaScript template literals in ES6',
body: 'Content of the post will be here...',
tags: ['es6', 'template literals', 'javascript']
};
Code language: JavaScript (javascript)
The following code returns the HTML code of the post object. Note that we use the object destructuring technique to assign the properties of the post object to individual variables : title, excerpt, body, and tags.
let {title, excerpt, body, tags} = post;let postHtml = `<article>
<header>
<h1>${title}</h1>
</header>
<section>
<div>${excerpt}</div>
<div>${body}</div>
</section>
<footer>
<ul>
${tags.map(tag => `<li>${tag}</li>`).join('\n ')}
</ul>
</footer>`;
Code language: HTML, XML (xml)
The following is the output of the variable postHtml. Notice how we used the spacing to indent the <li> tags correctly.
<article>
<header>
<h1>JavaScript Template Literals</h1>
</header>
<section>
<div>Introduction to JavaScript template literals in ES6</div>
<div>Content of the post will be here...</div>
</section>
<footer>
<ul>
<li>es6</li>
<li>template literals</li>
<li>javascript</li>
</ul>
</footer>Code language: HTML, XML (xml)
Variable and expression substitutions
At this point, a template literal is just like a better version of a regular JavaScript string. The big difference between a template literal and a regular string is substitutions.
The substitutions allow you to embed variables and expressions in a string. The JavaScript engine will automatically replace these variables and expressions with their values. This feature is known as string interpolation.
To instruct JavaScript to substitute a variable and expression, you place the variable and expression in a special block as follows:
${variable_name}
See the following example:
let firstName = 'John',
lastName = 'Doe';let greeting = `Hi ${firstName}, ${lastName}`;
console.log(greeting); // Hi John, Doe
Code language: JavaScript (javascript)
The substitution ${firstName} and ${lastName} access the variables firstName and lastName to insert their values into the greeting string.
The greeting variable then holds the result of the substitutions. The following example substitutes an expression instead:
let price = 8.99,
tax = 0.1;let netPrice = `Net Price:$${(price * (1 + tax)).toFixed(2)}`;
console.log(netPrice); // netPrice:$9.89
Code language: JavaScript (javascript)
Tagged templates
A template tag carries the transformation on the template literal and returns the result string.
You place the tag at the beginning of the template before the backtick (`) character as follows:
let greeting = tag`Hi`;Code language: JavaScript (javascript)
In this example, tag is the template tag that applies to the Hi template literal. The tag can be any function with the following signature:
function tag(literals, ...substitutions) {
// return a string
}Code language: JavaScript (javascript)
In this function:
- The
literalsparameter is an array that contains the literal strings. - The
substitutionsparameter contains the subsequent arguments interpreted for each substitution.
See the following example:
function format(literals, ...substitutions) {
let result = ''; for (let i = 0; i < substitutions.length; i++) {
result += literals[i];
result += substitutions[i];
}
// add the last literal
result += literals[literals.length - 1];
return result;
}
let quantity = 9,
priceEach = 8.99,
result = format`${quantity} items cost $${(quantity * priceEach).toFixed(2)}.`;
console.log(result); // 9 items cost $80.91.
Code language: JavaScript (javascript)
In this example, the format() function accepts three arguments: the literals array and two other arguments stored in the substitutions array.
The first argument is the literals array that contains three elements:
- An empty string before the first substitution (”). Note that the first argument of the literals array is an empty string.
- A string
'items cost'that locates between the first and the second substitutions. - A string that follows the second substitution (
'.')
The second argument is 9, which is the interpreted value of the quantity variable. It becomes the first element of the substitutions array. The third argument is 80.91, which is the interpreted value of the expression (quantity * priceEach).toFixed(2). It becomes the second element of the substitutions array.
Summary
- Use the backtick to create a string literal for string interpolation.