json-vars

Enables the use of variables in JSON and JSON-like configuration files

Install with

npm i --save json-vars

Example usage

const jVars = require('json-vars')

const config = {
  foo: {
    bar: '${env:BAR|default("bar")}'
  },
  baz: 'foo.bar is equal to ${self:foo.bar}'
}

jVars.resolve(config).then( res => console.log(res) )
// Output => {
//             foo: {
//               bar: 'bar'
//             },
//             baz: 'foo.bar is equal to bar'
//           }

Syntax

Variable

Transformer

Scope, Variable and Transformer's names can contain any letter, number, -, . or _.

An Argument can be any string, number or boolean. String Arguments can contain the same character set of names.

If it's needed, a Variable's name or a string Argument can be wrapped in single or double quotes, in which case any character is allowed.

Scope

The Scope indicates to json-vars the context on which it should resolve the Variable's name.

Transformer

A Transformer can modify the value coming from the Scope before the final substitution happens. If multiple Transformers are chained, they are applied left to right.

Nesting Variables

Variables can also be placed inside a Variable's name or a string Argument, this works only for unquoted strings.

So in "${self:foo.${env:ENV_VAR}}" the inner Variable will be resolved and replaced before the outer variale, while in "${self:'foo.${env:ENV_VAR}'}" the outer Variable's name will be left as is.

Variable interpolation

Once a Variable is resolved, its placeholder gets replaced with its resolved value.

There are two possible replacement methods:

• If the Variable was contained in a longer string, the resolved value is stringified and then replaced.
• If the Variable's placeholder exactly match the string that contains it, the resolved value is returned as is and its type is preserved.

Example

{
  "num": 42,
  "stringified": "num is ${self:num}",
  "preserved": "${self:num}"
}
// becomes
{
  "num": 42,
  "stringified": "num is 42",
  "preserved": 42
}

Builtin Scopes and Transformers

Scopes

env

Resolves the Variable against the current shell environment.

self

References another property of the current input object.

Transformers

default(<defaultValue>)

Recover failures and return defaultValue, otherwise it has no effect.

Running the tests

To run tests:

npm test

And coding style tests

Run NSP and TSLint

npm run lint