JSON Conditions

JSON/YAML conditional evaluations with and, or, not, and equals.

Example:

const conditions = require('json-conditions');

const syntax = {
  doILikeConditions: {
    not: {
      equal: [
        {field: oneVariable},
        {field: anotherVariable}
      ]}
  },
  doILoveConditions: {
    and: [
      {equal: [
        {field: someStringValue},
        {value: 'literal'}
      ]},
      {equal: [
        {field: someBooleanValue},
        {value: true}
      ]}
    ]
  }
};

const fieldData = {
  someStringValue: 'literal',
  someBooleanValue: true,
  oneVariable: 'hello',
  anotherVariable: 'goodbye'
};

function resolveField(n) {
  if (fieldData.hasOwnProperty(n)) {
    return n;
  }
  throw new Error(`Unknown field: ${n}`)
}

const result = conditions.evaluate(resolveField, syntax);

console.log(result.doILikeConditions); // false
console.log(result.doILoveConditions); // true

Methods

evaluate(fieldResolverFn, conditionsObj)

Evaluates each condition to its final true/false value. Fields are resolved by calling the passed-in fieldResolverFn.

Since your field values may be stored in a Map, a database ORM object or perhaps a basic Object, you must provide your own resolver function which returns the value for a given fieldName. The resolver function should match the signature:
fieldResolverFn(fieldName) => field value as boolean | string | number | null

For a usage example see above.

listFields(conditionsObj)

Finds all {field: 'name'} references, and returns an array with all found field names within any condition.

const conditions = require('json-conditions');

const fieldNames = conditions.listFields({
  firstCond: {
    and: [
      {equal: [
        {field: 'fieldOne'},
        {field: 'fieldTwo'}
      ]},
      {equal: [
        {field: 'fieldThree'},
        {value: 3}
      ]}
    ]
  },
  secondCond: {
    or: [
      {equal: [
        {field: 'fieldThree'},
        {value: 3}
      ]},
      {equal: [
        {field: 'fieldFour'},
        {value: 4}
      ]}
    ]
  }
});

console.log(fieldNames); // [ 'fieldOne', 'fieldTwo', 'fieldThree', 'fieldFour' ]

validate(conditionsObj)

Validates the condition object, and throws an error if the syntax is not valid. The error object will include a .errors property with an array of validation errors.

Example

const conditions = require('json-conditions');

conditions.validate({
  invalidCondition: {
    and: []
  }
}); // throws an Error, because 'and' must have at least two parameters

Condition Syntax

equal

{equal: [valueA, valueB]}

• Only accepts two values
• Each value can be a literal value or a field value
  • Field value {field: 'fieldName}, where value is resolved by function passed to evaluate()
  • Literal value {value: 'hello'}, the value can be in the following forms:
    • Boolean: {value: true} {value: false}
    • Null: {value: null}
    • Number: {value: 32}
    • String: {value: 'string'}
• Returns true if both values are strictly equal ===

Examples

// ensure two fields exactly match
{equal: [
  {field: 'firstField'},
  {field: 'secondField'}
]}
// ensure a field matches a literal value
{equal: [
  {field: 'firstField'},
  {value: 'literal-value'}
]}

and

{and: [...conditions]}

• Must have at-least 2 conditions, but can have more
• Each condition can be an and, or, not, or equal statement
• Returns true only if all conditions are true

Examples

// true if the two fields exactly match
// AND the third field equals 'test'
{and: [
  {equal: [
    {field: 'firstField'},
    {field: 'secondField'}
  ]},
  {equal: [
    {field: 'thirdField'},
    {value: 'test'}
  ]},
]}

or

{or: [...conditions]}

• Must have at-least 2 conditions, but can have more
• Each condition can be an and, or, not, or equal statement
• Returns true if any conditions are true

Examples

// true if the two fields exactly match
// OR the third field equals 'test'
{or: [
  {equal: [
    {field: 'firstField'},
    {field: 'secondField'}
  ]},
  {equal: [
    {field: 'thirdField'},
    {value: 'test'}
  ]},
]}

not

{not: condition}

• Expects a single condition
• Condition can be an and, or, not, or equal statement
• Returns the opposite of the condition

Examples

// false if both fields exactly match
// true if the fields do not match
{not: {equal: [
  {field: 'firstField'},
  {field: 'secondField'}
]}}