JavaScript Fundamentals · Variables & Data Types · Lesson 5 of 48
Type Conversion
Concept
Type Conversion
JavaScript often converts types automatically, which is called coercion. You can also convert explicitly with Number(), String(), and Boolean(), which is usually safer since the result is predictable.
By the end of this lesson
- Explain the core idea behind Type Conversion.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Syntax
Number(value)
String(value)
Boolean(value)ExampleRunnable
let input = "42";
let number = Number(input);
console.log(number + 8);A classic coercion surprise
console.log("5" + 3); // "53" (string concatenation)
console.log("5" - 3); // 2 (numeric subtraction)Note: The + operator concatenates when either side is a string, but - always tries to convert both sides to numbers first.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Type Conversion. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Convert the string "100" to a number and add 25 to it.
Loading editor…
Console