JS Daily 21 - Tagged Template Literal

Last updated on 11 Dec, 2020

What is the output of following code?

const formatString = (strings, ...values) => {
  return strings.join(",") + values.join(",");

const name = "Backbencher";
const age = 2;

const result = formatString `${name} is ${age} years old`;


Output is ", is , years oldBackbencher,2"

This is an example of Tagged Template literal. Here the template literal string is sliced and passed to the tagged function(formatString).

At first the string is sliced like |${name}| is |${age}| years old. Then all the string literals are grouped to one array(["", " is ", " years old"]). The values are picked and send to the function as second argument, third argument and so on. We gather all the arguments except first, using ...values. So now values contains an array of 2 elements.

The return value of the formatString() call, is assigned to result.

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Joby Joseph
Web Architect