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number

Accepts finite numbers (can be integer or float values). Values NaN, or positive and negative Infinity will get rejected. 
const number: Decoder<number>

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Validation Rules

  • Must be a JavaScript number type
  • Must be finite (rejects NaN, Infinity, and -Infinity)
  • Accepts both integers and floats
  • Accepts negative and positive numbers

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Examples

import { number } from 'decoders';

const result1 = number.decode(42);        // ✓ Ok(42)
const result2 = number.decode(-3.14);     // ✓ Ok(-3.14)
const result3 = number.decode(0);         // ✓ Ok(0)
const result4 = number.decode(NaN);       // ✗ Error: "Number must be finite"
const result5 = number.decode(Infinity);  // ✗ Error: "Number must be finite"
const result6 = number.decode("42");      // ✗ Error: "Must be number"

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Use Cases

  • General numeric values
  • Calculations and measurements
  • Coordinates and positions
  • Default choice for most number validations

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anyNumber

Accepts any valid number value. This also accepts special values like NaN and Infinity. Unless you want to deliberately accept those, you’ll likely want to use the number decoder instead. 
const anyNumber: Decoder<number>

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Validation Rules

  • Must be a JavaScript number type
  • Accepts NaN, Infinity, and -Infinity
  • Accepts all finite numbers

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Examples

import { anyNumber } from 'decoders';

const result1 = anyNumber.decode(42);        // ✓ Ok(42)
const result2 = anyNumber.decode(NaN);       // ✓ Ok(NaN)
const result3 = anyNumber.decode(Infinity);  // ✓ Ok(Infinity)
const result4 = anyNumber.decode(-Infinity); // ✓ Ok(-Infinity)
const result5 = anyNumber.decode("42");      // ✗ Error: "Must be number"

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Use Cases

  • Mathematical operations that may produce NaN or Infinity
  • Serialization/deserialization where special values are valid
  • Low-level number processing

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numeric

Accepts valid numerical strings (in base-10) and returns them as a number. To only accept numerical strings and keep them as string values, use the decimal decoder. 
const numeric: Decoder<number>

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Validation Rules

  • Must be a string type
  • Must contain only decimal digits (0-9)
  • Returns the parsed number value
  • Uses base-10 conversion

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Examples

import { numeric } from 'decoders';

const result1 = numeric.decode("42");      // ✓ Ok(42)
const result2 = numeric.decode("0");       // ✓ Ok(0)
const result3 = numeric.decode("123");     // ✓ Ok(123)
const result4 = numeric.decode("-42");     // ✗ Error: "Must only contain digits"
const result5 = numeric.decode("3.14");    // ✗ Error: "Must only contain digits"
const result6 = numeric.decode(42);        // ✗ Error (expects string input)

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Use Cases

  • Parsing numeric strings from forms
  • URL parameters that should be numbers
  • String-based API responses with numeric values
  • CSV or text file parsing
  • decimal - Accepts numeric strings but keeps them as strings
  • number - For direct number values (not strings)

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Type Hierarchy

The number decoders follow this hierarchy: 
anyNumber (all number values including NaN, Infinity)
  └── number (finite numbers only)
       ├── integer (whole numbers)
       │    └── positiveInteger (non-negative whole numbers)
       └── positiveNumber (non-negative numbers)
Each level adds additional constraints on top of the previous level.

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