Type Conversion

JavaScript can convert values between types, both automatically and by hand.

Convert to string

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### String(123);     // "123"
(123).toString(); // "123"

### String(true);    // "true"

Convert to number

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### Number("123");  // 123

### Number("3.14"); // 3.14

### Number("");     // 0

### Number("abc");  // NaN

Convert to boolean

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### Boolean(1);    // true

### Boolean(0);    // false

### Boolean("");   // false

### Boolean("hi"); // true

Implicit conversion

JavaScript converts types automatically in many situations:

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"5" + 1; // "51"  (the + joins as strings)
"5" - 1; // 4     (the - forces numbers)

Why conversion matters

Forms give you strings. If you need numbers, convert them first:

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let value = "10";

### Number(value) + 5; // 15

TL;DR

• String(), Number(), Boolean() convert explicitly.
• The + operator joins strings.
• - * / force numbers.
• Always convert form input before math.