Expression-expander NPM

Expression Expander

Expands \${to be evaluated} expressions in object graphs. The actual expression syntax inside of the \${evaluated} is not defined within this module (only simple key lookup)

example

file.js

import { createContext } from "expression-expander";

const context = createContext();

context.properties = { aKey: "aValue", moreKeys: { a: 1, b: 2 } };

// expanding whole expressions at the key position
console.log(
  JSON.stringify(
    context.expand({ simple: "${aKey}", complex: { "${moreKeys}": {} } })
  )
);

Output

{ "simple": "aValue", "complex": { "a": 1, "b": 2 } }

Any Object of the following types may be expanded

String
Number
BigInt
Buffer
Object (key and value will be expanded)
Array
Map (key and value will be expanded)
Set
Boolean
Promise

API

Evaluator

Type: Function

Parameters

expression string
context Object
path [PathEntry]

Returns Object expression evaluation result

PathEntry

Type: Object

Properties

value Object

Quoter

Type: Function

Parameters

value string to be quoted

Returns string quoted value

Expander

Type: Function

Parameters

value (string | boolean | number | bigint | Object | Map | Set)
path Array<PathEntry>?

ExpressionExpander

Type: Object

Properties

properties Object
expand Expander

createContext

Creates a new expansion context

Parameters

options Object? object with the following keys
- options.leftMarker string? lead in of expression
- options.rightMarker string? lead out of expression
- options.markerRegexp RegExp? expression with lead in / out
- options.valueQuoter Quoter? to quote expanded values by default no special quoting is done and the evaluated result will be direcly inserted into the output string
- options.evaluate Evaluator? evaluate(expression,context,path) function to evaluate expressions the default evaluation function does a lookup into the properties
- options.keepUndefinedValues boolean? true: is expression resolves to undefind the original string will be used (with surrounding ${})
- options.maxNestingLevel number? max number of recursive calls to expand defaults to 20
- options.properties Object? default properties to evaluate expression against