index.ts

import jsep from 'jsep';

/**
 * Evaluation code from JSEP project, under MIT License.
 * Copyright (c) 2013 Stephen Oney, http://jsep.from.so/
 */

// Default operator precedence from https://github.com/EricSmekens/jsep/blob/master/src/jsep.js#L55
const DEFAULT_PRECEDENCE = {
  '||': 1,
  '&&': 2,
  '|': 3,
  '^': 4,
  '&': 5,
  '==': 6,
  '!=': 6,
  '===': 6,
  '!==': 6,
  '<': 7,
  '>': 7,
  '<=': 7,
  '>=': 7,
  '<<': 8,
  '>>': 8,
  '>>>': 8,
  '+': 9,
  '-': 9,
  '*': 10,
  '/': 10,
  '%': 10
};

const binops = {
  '||': function (a, b) { return a || b; },
  '&&': function (a, b) { return a && b; },
  '|': function (a, b) { return a | b; },
  '^': function (a, b) { return a ^ b; },
  '&': function (a, b) { return a & b; },
  '==': function (a, b) { return a == b; }, // jshint ignore:line
  '!=': function (a, b) { return a != b; }, // jshint ignore:line
  '===': function (a, b) { return a === b; },
  '!==': function (a, b) { return a !== b; },
  '<': function (a, b) { return a < b; },
  '>': function (a, b) { return a > b; },
  '<=': function (a, b) { return a <= b; },
  '>=': function (a, b) { return a >= b; },
  '<<': function (a, b) { return a << b; },
  '>>': function (a, b) { return a >> b; },
  '>>>': function (a, b) { return a >>> b; },
  '+': function (a, b) { return a + b; },
  '-': function (a, b) { return a - b; },
  '*': function (a, b) { return a * b; },
  '/': function (a, b) { return a / b; },
  '%': function (a, b) { return a % b; }
};

const unops = {
  '-': function (a) { return -a; },
  '+': function (a) { return +a; },
  '~': function (a) { return ~a; },
  '!': function (a) { return !a; },
};

declare type operand = number | string;
declare type unaryCallback = (a: operand) => operand;
declare type binaryCallback = (a: operand, b: operand) => operand;

type AnyExpression = jsep.ArrayExpression
  | jsep.BinaryExpression
  | jsep.MemberExpression
  | jsep.CallExpression
  | jsep.ConditionalExpression
  | jsep.Identifier
  | jsep.Literal
  | jsep.LogicalExpression
  | jsep.ThisExpression
  | jsep.UnaryExpression;

function evaluateArray(list, context) {
  return list.map(function (v) { return evaluate(v, context); });
}

async function evaluateArrayAsync(list, context) {
  const res = await Promise.all(list.map((v) => evalAsync(v, context)));
  return res;
}

function evaluateMember(node: jsep.MemberExpression, context: object) {
  const object = evaluate(node.object, context);
  let key: string;
  if (node.computed) {
    key = evaluate(node.property, context);
  } else {
    key = (node.property as jsep.Identifier).name;
  }
  if (/^__proto__|prototype|constructor$/.test(key)) {
    throw Error(`Access to member "${key}" disallowed.`);
  }
  return [object, object[key]];
}

async function evaluateMemberAsync(node: jsep.MemberExpression, context: object) {
  const object = await evalAsync(node.object, context);
  let key: string;
  if (node.computed) {
    key = await evalAsync(node.property, context);
  } else {
    key = (node.property as jsep.Identifier).name;
  }
  if (/^__proto__|prototype|constructor$/.test(key)) {
    throw Error(`Access to member "${key}" disallowed.`);
  }
  return [object, object[key]];
}

function evaluate(_node: jsep.Expression, context: object) {

  const node = _node as AnyExpression;

  switch (node.type) {

    case 'ArrayExpression':
      return evaluateArray(node.elements, context);

    case 'BinaryExpression':
      return binops[node.operator](evaluate(node.left, context), evaluate(node.right, context));

    case 'CallExpression': {
      let caller, fn, assign;
      if (node.callee.type === 'MemberExpression') {
        assign = evaluateMember(node.callee as jsep.MemberExpression, context);
        caller = assign[0];
        fn = assign[1];
      } else {
        fn = evaluate(node.callee, context);
      }
      if (typeof fn !== 'function') { return undefined; }
      return fn.apply(caller, evaluateArray(node.arguments, context));
    }

    case 'ConditionalExpression':
      return evaluate(node.test, context)
        ? evaluate(node.consequent, context)
        : evaluate(node.alternate, context);

    case 'Identifier':
      return context[node.name];

    case 'Literal':
      return node.value;

    case 'LogicalExpression':
      const leftValue = evaluate(node.left, context);
      if (node.operator === '||' && leftValue) {
        return leftValue;
      } else if (node.operator === '&&' && !leftValue) {
        return leftValue;
      }
      return binops[node.operator](leftValue, evaluate(node.right, context));

    case 'MemberExpression':
      return evaluateMember(node, context)[1];

    case 'ThisExpression':
      return context;

    case 'UnaryExpression':
      return unops[node.operator](evaluate(node.argument, context));

    default:
      return undefined;
  }

}

async function evalAsync(_node: jsep.Expression, context: object) {

  const node = _node as AnyExpression;

  // Brackets used for some case blocks here, to avoid edge cases related to variable hoisting.
  // See: https://stackoverflow.com/questions/57759348/const-and-let-variable-shadowing-in-a-switch-statement
  switch (node.type) {

    case 'ArrayExpression':
      return await evaluateArrayAsync(node.elements, context);

    case 'BinaryExpression': {
      const [left, right] = await Promise.all([
        evalAsync(node.left, context),
        evalAsync(node.right, context)
      ]);
      return binops[node.operator](left, right);
    }

    case 'CallExpression': {
      let caller, fn, assign;
      if (node.callee.type === 'MemberExpression') {
        assign = await evaluateMemberAsync(node.callee as jsep.MemberExpression, context);
        caller = assign[0];
        fn = assign[1];
      } else {
        fn = await evalAsync(node.callee, context);
      }
      if (typeof fn !== 'function') {
        return undefined;
      }
      return await fn.apply(
        caller,
        await evaluateArrayAsync(node.arguments, context)
      );
    }

    case 'ConditionalExpression':
      return (await evalAsync(node.test, context))
        ? await evalAsync(node.consequent, context)
        : await evalAsync(node.alternate, context);

    case 'Identifier':
      return context[node.name];

    case 'Literal':
      return node.value;

    case 'LogicalExpression': {
      if (node.operator === '||') {
        const left = await evalAsync(node.left, context);
        if (left) {
          return left;
        }
        return await evalAsync(node.right, context);
      } else if (node.operator === '&&') {
        const left = await evalAsync(node.left, context);
        if (!left) {
          return left;
        }
        return await evalAsync(node.right, context);
      }

      const [left, right] = await Promise.all([
        evalAsync(node.left, context),
        evalAsync(node.right, context)
      ]);

      return binops[node.operator](left, right);
    }

    case 'MemberExpression':
      return (await evaluateMemberAsync(node, context))[1];

    case 'ThisExpression':
      return context;

    case 'UnaryExpression':
      return unops[node.operator](await evalAsync(node.argument, context));

    default:
      return undefined;
  }
}

function compile(expression: string | jsep.Expression): (context: object) => any {
  return evaluate.bind(null, jsep(expression));
}

function compileAsync(expression: string | jsep.Expression): (context: object) => Promise<any> {
  return evalAsync.bind(null, jsep(expression));
}

// Added functions to inject Custom Unary Operators (and override existing ones)
function addUnaryOp(operator: string, _function: unaryCallback): void {
  jsep.addUnaryOp(operator);
  unops[operator] = _function;
}

// Added functions to inject Custom Binary Operators (and override existing ones)
function addBinaryOp(operator: string, precedence_or_fn: number | binaryCallback, _function: binaryCallback): void {
  if (_function) {
    jsep.addBinaryOp(operator, precedence_or_fn as number);
    binops[operator] = _function;
  } else {
    jsep.addBinaryOp(operator, DEFAULT_PRECEDENCE[operator] || 1);
    binops[operator] = precedence_or_fn;
  }
}

export {
  jsep as parse,
  evaluate as eval,
  evalAsync,
  compile,
  compileAsync,
  addUnaryOp,
  addBinaryOp
};