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TypeScript - Interpolated Strings


Coming from the .NET world String.Format() was by far my most used function for generating user readable error / log messages. After jumping over to TypeScript, I was bummed to learn that no similar function existed. However, it wasn’t so bad, after all console.log() allows us to pass multiple parameters and has no trouble logging them.

let foo = { bar: 1 };
console.log("Foo is ", foo);
//Prints: Foo is Object { bar : 1 }

But this only covers one of the many use cases I used String.Format() for. Disappointed with TypeScript, I decided to do some searching online. Surely I couldn’t be the only one with this frustration?

Thanks to my scrutinizing research efforts (aka a couple Google searches) I discovered it was not TypeScript that was lacking, but instead it was a failure on my part to understand string interpolation. Things didn’t really click until I came across a StackOverflow question from someone else who was facing a similar issue. The top answer of the post advised them to use string interpolation.

String interpolation sounds intimidating. I actually remember reading about it awhile ago when I came across an article covering the new features of C# 6.0. At the time however, it never clicked to me how useful it truly was and I assumed it was simply above my pay-grade.

Without String.Format() as my crutch though, my only other option was to manually join strings together and it felt gross.

let foo = { bar: 1 };
alert("Foo is " + + ".");

I decided to look up the definition of interpolation since it sounded like jargon to me. Google defines interpolation as:


  1. the insertion of something of a different nature into something else.

Hmm, that sounds kinda useful. A bit more research and I learned that in JavaScript / TypeScript they are referred to as template strings. And just like that, the fog of several months of ignorance lifted. All this time I had been overlooking such a simple concept because it had a daunting name.

String interpolation had fallen victim to the classic Computer Science theme of overly complicated, jargony names for simple concepts such as Dependency Injection.

String interpolation allow us to create strings using local variables as if we were writing a standard line of code.

let name = "Bert";
console.log(`Hello there ${name}!`);
//Prints: Hello there Bert!

The only requirement to use them in TypeScript is to change the quotation marks surronding the string to the backquote character `. Then anytime we want to insert a value into the string we use the ${} syntax.

When inside a ${} we can even use class methods.

    let name = 'Bert';
    console.log('HI ${name.toUpperCase()});
    //Prints: HI BERT

Functions are also fair game.

function doubleIt(value: Number): number {
  return value * 2;

console.log(`2 * 2 is ${doubleIt(2)}`);
//Prints: 2 * 2 is 4

And lastly, if we wanted to print a variable but we are unsure if the variable is null, we could perform a quick null check directly in the string.

    let name = null;
    console.log(`Players name is: ${name || 'Unknown'});
    //Prints: Players name is Unknown

Interpolated strings have quickly grown to be one my favorite features. Even on the C# side I find myself using interpolated strings over String.Format() as it feels cleaner in my opinion. Looking back my only regret is not giving string interpolation a chance sooner. I mistakenly judged a book by it’s cover instead of taking the time to learn more.