squid-eval

Writing logic in natural language way. (Could use eval() function of JS, but it can lead to code injection)

• Simple expression/rule evaluator with minimal syntax.
• Write expression in natural language.
• Write conditional logic or math calculation or both.
• Easily use in front-end or back-end.
• Reduce the coding effort with the logic written as Json or DB data.
• Can use this to show a conditional content/input-field on UI.
• Customize operators symbols.

How it works

import { RuleEvaluator } from 'squid-eval'

const evaluator = new RuleEvaluator();
evaluator.parse('Toronto Rule', "[city] = Toronto and [day of birth] > 20 or [name] = Wendy's");

console.log(evaluator.execute('Toronto Rule', {
    city: 'Toronto',
    'day of birth': 23,
    name: "Wendy's"
}));
// output will be true

Handles parenthesized expressions as well.

evaluator.parse('Toronto 2nd Rule', "[city] = Toronto and ([day of birth] + 10 < 20 or [name] = Wendy's)");
console.log(evaluator.execute('Toronto Rule', {
    city: 'Toronto',
    'day of birth': 23,
    name: "Starbucks"
}));
// output will be false

Syntax

Only two things to know

• Variables are to be put within square brackets. e.g. [day of birth]
• If need to use operator symbols or square brackets as a plain text, then just put it in side single quotes. e.g. [formula] = '2 + [3]'. And to use quote inside quoted text, just use it twice. e.g. [name] = 'Macy''s'

Validation

• Call parse() method which will throw error if expression has issue.
• Call getVariables() and check if the required variables are extracted.

Customizing operators

Default operators available are: +, -, *, /, =, !=, >, <, and, or, contains Want to add more of your own? Below are the APIs can be used.

• addOperator() to add a new operation
• deleteOperator() to delete an operator
• clearOperators() to delete all the operators
• changeOperatorSymbol() to change symbol of an existing operator. e.g. say you don't like to use '=', instead would prefer using 'is' as in a rule '[city] is Toronto'

Rule Action Service

Optional service to evaluate rules and find actions to take.

• RuleActionService:
  • add (ruleName, action: string, rule: string)
  • update (ruleName, action: string, rule: string)
  • delete (ruleName, action: string)
  • evaluate (ruleName, data: JsonType): string[] Returns list of actions, to be taken based on rules setup for given rule name.
  • evaluateAll (data: JsonType): Map<RuleName, string[]> Return list of actions to be taken on each of the saved rule names.

const inputFieldActionsService = new RuleActionService(); inputFieldActionsService.add('underAgeDisclaimer', 'show', '[age] < 18'); inputFieldActionsService.add('underAgeDisclaimer', 'block-user', '[age] < 16');

const formData = { age: 15 }; inputFieldActionsService.evaluate('underAgeDisclaimer', formData); // ['show', 'block-user']