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ECMAScript 6 Power Tutorial: Template Strings

This post is part of a series called ECMAScript 6 Power Tutorial.
ECMAScript 6 Power Tutorial: Class and Inheritance
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Welcome to the second part of my series about ECMAScript 6! One of my favorite new web standards of Microsoft Edge, the new browser rendering engine we’re creating at Microsoft, is the extensive support it offers for ECMAScript 6. So I wrote this series to walk you through some of the cool things you can do with ECMAScript 6 when writing large applications for the web.

In the first installment, I covered Class and Inheritance. In this article, I’ll focus on template strings based on my personal experience creating embedded expressions.

Resolving the Line Return Problem

When working on Babylon.js, I have to deal with shaders code which can be seen, for the sake of comprehension, like a big bunch of text (which looks like C).

You can find an example in this GitHub repository.

The problem when dealing with long text in JavaScript is the line return. How many times have you written this kind of thing?

When you have to work with shaders that are 200+ lines long, this quickly becomes a real pain.

Thankfully, ECMAScript 6 comes with the new template strings feature. Among other wonders, a template string directly supports multiline strings:

Because all characters are significant inside a template string, I cannot add leading whitespaces.

Now as JavaScript developers we have three ways to define strings:

  • with “”
  • with ‘’
  • with `` (also known as back-tick or grave accent)

So What About the Template Part Then?

Multiline support is not the only feature of template strings. Indeed, you can also use template strings to substitute placeholders with variables values, as you may have done with printf in C/C++ or string.Format in C#:

This code produces the following output:

Pretty handy, right?

Remember the ECMAScript 5 way:

Going Further With Tags

The final stage of template strings specification is about adding a custom function before the string itself to create a tagged template string:

The function here is used to get access to both the constant string part and the evaluated variables values.

In the previous example, strings and values are the following:

  • strings[0] = “You have “ 
  • values[0] = 3 
  • strings[1] = “items in your basket for a total of $” 
  • values[1] = 100.5 
  • strings[2] = “”

As you can see, every values[n] is surrounded by constants strings (strings[n] and strings[n + 1]).

This allows you to control how the final output string is built. In my previous example, I only reproduced the basic behavior of template strings, but we can go further and add cool processing on your string.

For instance, here is a piece of code to block strings that try to inject custom DOM elements:

Tagged template strings can be used for a lot of things like security, localization, creating your own domain specific language, etc.

Raw Strings

Tag functions have a special option when accessing strings constants: They can use strings.raw to get the unescaped string values. For instance, in this case \n will not be seen as only one character but actually two: \ and n.

The main goal is to allow you to access the string as it was entered:

This code generates the following output:

You can also use a new function of String: String.raw(). This function is a built-in function that does exactly what my previous example does:


Microsoft Edge and the latest versions of Chrome (41+), Opera(28+) and Firefox (35+) support template strings, and you can track the level of overall ECMAScript 6 support here. So if you are targeting the modern web, there is no reason not to embrace template strings.

For a full view of what new web standards and features are coming in Microsoft Edge—like WebAudio—you can see the full list at dev.modern.ie/platform/status.

More Hands-On With JavaScript

It might surprise you a bit, but Microsoft has a bunch of free learning on many open source JavaScript topics, and we’re on a mission to create a lot more with Microsoft Edge. Check out my own:

Or our team’s learning series:

And some free tools: Visual Studio Community, Azure Trial, and cross-browser testing tools for Mac, Linux, or Windows.

This article is part of the web dev tech series from Microsoft. We’re excited to share Microsoft Edge and the new EdgeHTML rendering engine with you. Get free virtual machines or test remotely on your Mac, iOS, Android, or Windows device @ http://dev.modern.ie/.

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