Jelly - JSON Expression Language

"Jelly", by my son Isaak

Built as a small side project because what else to do on a lazy sunday afternoon :) ?

Why Jelly?

Jelly expressions are simple expressions built in JSON that can be used to perform validation, filtering, calculated fields, authorization checks...

While Jelly expressions can be run from code (see examples below), we think (hope) they will typically be used in "scratch like" applications to allow end users to easily build queries, filters etc...

Expression types

There exist all kind of expressions (e.g. logical operator expressions, math expressions, comparison expressions) and we plan to add more.

Currently we have:

• logical operator expressions: and, or, not
• math expressions: sum, multiply
• comparison expressions: eq, gt, gte, nil

More info: https://github.com/david-bulte/jelly/blob/master/src/jelly.domain.ts

Examples

Here some examples copied from the test suite:

Simple sum:

    const expr: Expr = {
      operator: 'sum',
      children: [1, 2, 3]
    };
    expect(evaluate(expr)).toBe(6)

Combining comparison and sum:

    const expr: Expr = {
        operator: 'eq',
        children: [3, {
            operator: 'sum',
            children: [1, 2]
        }]
    };
    expect(evaluate(expr)).toBe(true)

Comparison expression with custom success and fail hooks (default success is true and fail is false):

    let expr: Expr = {
      operator: 'eq',
      children: [1, 1],
      success: ':)',
      fail: ':('
    };
    expect(evaluate(expr)).toBe(':)')
    
    expr = {
      operator: 'eq',
      children: [1, 2],
      success: ':)',
      fail: ':('
    };
    expect(evaluate(expr)).toBe(':(')

One can pass a context to the evaluate function. String expressions (wrapped in {{ and }}) can obtain values from this context.

    const expr: Expr = {
      operator: 'eq',
      children: ['coffee', '{{person.favoriteDrink}}']
    };
    expect(evaluate(expr, {person: {name: 'Dale Cooper', favoriteDrink: 'coffee'}})).toBe(true)

A more complex example:

    const expr: Expr = {
      operator: 'sum',
      children: [
        {
          operator: 'gt',
          children: [
            {
              operator: 'sum',
              children: [
                {operator: 'eq', children: ['{{form.input1.value}}', 2], success: 1, fail: 0},
                {operator: 'eq', children: ['{{form.input2.value}}', 2], success: 1, fail: 0},
              ],
            },
            1,
          ],
          success: 3,
          fail: 0,
        },
        {operator: 'eq', children: ['{{form.input1.value}}', 3], success: 6, fail: 0},
        {operator: 'eq', children: ['{{form.input2.value}}', 3], success: 2, fail: 0},
      ],
    };
    
    const form = {input1: {value: 3}, input2: {value: 2}};
    expect(evaluate(expr, {form})).toBe(6)