safe-evaluate-expression

safe-evaluate-expression

Small library to dynamically create and evaluate expression with multiple parameters (even undefined). It also offer an ancillary function to protect lambda function to undefined params inputs.

Installation

npm install safe-evaluate-expression

Usage

evaluate(expression:[String], params:[Object])

Example

const evaluate = require("safe-evaluate-expression");
evaluate("a > 1", { a: 3 }); // -> true

Advanced Example

const evaluate = require("safe-evaluate-expression");

const operators = {
  isUndefined: (x) => x === undefined,
  isEqual: (a, b) => a === b,
  isGreater: (a, b) => a > b,
  isLower: (a, b) => a < b,
};

const vars = { a: 1, b: 1, c: 2 };
const params = { ...vars, ...operators };

evaluate("isEqual(a,b)", params); // -> true
evaluate("isEqual(a,c)", params); // -> false
evaluate("isEqual(a,notDefined)", params); // -> false
evaluate("isUndefined(a)", params); // -> false
evaluate("isUndefined(notDefined)", params); // -> true

// It works also with infinite nested conditions
evaluate("(isUndefined(notDefined) || (isGreater(c, a) && isLower(b, c))) && isEqual(a,1)", params); // -> true

Default lambda undefined params

protectedLambda(lamdaFunc, [undefined dafalut])

Protect lambda function by assigning a default value for undefined input paramters.

const { defaultLambda } = require("safe-evaluate-expression");

const lambda = (a, b, c) => a + b + c;
const protectedLambda = defaultLambda(lambda, 0);

// The unprotected lambda returns NaN because all values are undefined
// The protected one return zero (default): 0 + 0 + 0
console.log(lambda(), protectedLambda()); // -> NaN 0