Documentation v1.2.1
Home GitHub

Type System

This page explains how NanoJSON derives a node's type from a JavaScript value, how each type is edited and serialized, what happens to an existing value on a type switch, and the null edge cases.

Type Derivation

On import, the type is derived at runtime by getType() (src/function/getType.js):

JS Value getType() Returns
Array.isArray(v) is true "array"
typeof v === "object" (including null) "object"
typeof v === "boolean" "boolean"
typeof v === "number" "number"
anything else "string"

Per-Type Behavior

Type Input Serialized As Notes
string textarea, multi-line The raw string —
number textarea, placeholder NUM Number(value) Input that can't parse as a number clears the field (except - and ., so negatives and decimals can be typed); an empty value serializes as 0
boolean true / false dropdown value.toLowerCase() === "true" An empty value is set to "true"
object No value input; shows children Object Unlimited nesting
array No value input; children shown by index with no key input Array Same
null — — Only produced by import; see "null Edge Cases" below

Switching Types

The type dropdown (src/function/typeSelect.js:25) offers only string / number / boolean / array / object — null cannot be selected manually. On a switch, the existing value is handled per target type (typeSelect.js:30-51):

Switch To Effect on the Existing Value
object / array value is cleared; if there are no children, one is added automatically (through #add, see Core Concepts)
number parseFloat on the existing string; cleared if unparseable. children are not cleared, so switching back to object / array restores them
string / boolean value and children are both cleared

After a switch, updateChild() rebuilds the node's DOM and triggers Lifecycle.update, then focus moves to the value-{id} element.

null Edge Cases

getType(null) returns "object" (JavaScript's typeof null === "object"), and the two call sites handle it inconsistently:

The actual results:

Imported Data Result
[null] Renders a string node containing the text "null"; serializes back as the string "null"
{"a": null} While rendering that node, showValue() in valueInput() calls .replace on null (src/function/valueInput.js:56, :80) and throws a TypeError; the initial render aborts and rendered never fires

If your data may contain null, convert it at the application layer (for example, to an empty string) before passing it to NanoJSON.

Further Reading

中文