Template Literals

Template literals use backticks and ${...} placeholders to embed evaluated expressions within strings.

What you will learn: the purpose of template literals, the rules TypeScript checks, and what its JavaScript behavior looks like in a runnable example.

They can span multiple lines and are especially useful for readable messages. Interpolation converts expressions to strings at runtime; do not confuse interpolation with TypeScript compile-time template literal types, which are a separate advanced type feature.

Key distinction: TypeScript checks the declared types during development; emitted JavaScript carries out the value-level operation at runtime. A type declaration alone never validates untrusted runtime input.

Read this illustration from the first labeled part to the last. Compare it with the example and identify which parts are type checks and which parts run in JavaScript.

This self-contained example uses fixed values, so it runs without reading input or depending on an external service. Paste it into the TypeScript Playground or save it as main.ts.

TypeScript program

const product = "Notebook";
const quantity = 3;
const unitPrice = 25;
console.log(`${quantity} × ${product}: ₹${quantity * unitPrice}`);

Verified output

3 × Notebook: ₹75

Run locally: npx tsc --strict --target es2022 --module commonjs main.ts, then node main.js. For projects with a tsconfig.json, build using that configuration instead.

JavaScript evaluates the three placeholders: quantity becomes 3, product becomes Notebook, and quantity × unitPrice becomes 75. It combines them into one displayed string.

Check each step: identify the input values, follow the JavaScript operation in execution order, and match the final expression with the exact output shown. An annotation can reject invalid source before execution, but does not change the value printed.

Single and double quoted strings do not evaluate ${...} placeholders. Use backticks, not quotes, for interpolation.

How to debug: reproduce the issue in a minimal example. For compiler errors, inspect the inferred and declared types; for a runtime surprise, log the actual values and follow their references or branches.

Create a sentence using a name, two numeric scores, and an arithmetic expression inside a template literal.

Practice routine: predict the result on paper, edit one part of the code, compile under --strict, run the JavaScript, and explain whether TypeScript caught an error or JavaScript simply behaved differently.

Template Literals: Template literals use backticks and ${...} placeholders to embed evaluated expressions within strings.

JavaScript evaluates the three placeholders: quantity becomes 3, product becomes Notebook, and quantity × unitPrice becomes 75. It combines them into one displayed string.

Before continuing, explain one valid use case, one common pitfall, and the separation between compile-time checking and runtime behavior for this feature.