Type conversion is the explicit transformation of a value from one type to another using built-in functions like String(), Number(), and Boolean().

User input comes as strings, API responses need parsing, and calculations require numbers. Type conversion bridges these gaps.

Think of type conversion like a universal adapter for electronics. You have a US plug (string) that needs to fit into a European socket (number). The adapter (conversion function) transforms it.

flowchart TD
    Input["User Input: '25' (string)"]
    Number["Number('25')"]
    Result["25 (number)"]
    Calculation["25 + 5 = 30"]

    Input --> Number --> Result --> Calculation

String(123);       // "123"
String(true);      // "true"
String(null);      // "null"
String(undefined); // "undefined"
String([1,2,3]);   // "1,2,3"

Number("123");     // 123
Number("12.5");    // 12.5
Number("abc");     // NaN
Number(true);      // 1
Number(false);     // 0
Number(null);      // 0
Number(undefined); // NaN

Boolean(1);        // true
Boolean(0);        // false
Boolean("hello");  // true
Boolean("");       // false
Boolean(null);     // false
Boolean(undefined);// false

• Always use explicit conversion — avoid relying on coercion
• Validate conversions, especially with user input
• Use parseInt() and parseFloat() for string parsing

Number("123abc"); // NaN — not 123!
parseInt("123abc"); // 123 — more forgiving

• Use String(), Number(), Boolean() for explicit conversion
• Always prefer explicit over implicit (coercion)
• Validate numeric conversions for user input

• MDN: Type Conversion