To help you get started, we've collected the most common ways that expression-eval is being used within popular public projects.

uber / deck.gl / modules / json / src / helpers / parse-expression-string.js View on Github

export default function parseExpressionString(propValue, configuration) {
  // NOTE: Can be null which represents invalid function. Return null so that prop can be omitted
  if (propValue in cachedExpressionMap) {
    return cachedExpressionMap[propValue];
  }

  let func;
  // Compile with expression-eval
  const ast = expressionEval.parse(propValue);
  if (!ast.right && !ast.left && ast.type === 'Identifier') {
    func = row => {
      return get(row, propValue);
    };
  } else {
    // NOTE: To avoid security risks, the arguments passed to the
    // compiled expression must only give access to pure data (no globals etc)
    // We disable function call syntax
    traverse(ast, node => {
      if (node.type === 'CallExpression') {
        throw new Error('Function calls not allowed in JSON expressions');
      }
    });
    // TODO Something like `expressionEval.eval(ast, {row});` would be useful for unpacking arrays
    func = row => {
      return expressionEval.eval(ast, row);

View more ways to use expression-eval

expression-eval

JavaScript expression parsing and evaluation.

⚠️ UNMAINTAINED: The expression-eval npm package is no longer maintained. The package was originally published as part of a now-completed personal project, and I do not have incentives to continue maintenance. Please feel free to use the code, but be aware that support and updates will not be available.

⚠️ SECURITY NOTICE: As mentioned under Security below, this library does not attempt to provide a secure sandbox for evaluation. Evaluation involving user inputs (expressions or values) may lead to unsafe behavior. If your project requires a secure sandbox, consider alternatives such as vm2.

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Installation

Install:

npm install --save expression-eval

Import:

// ES6
import { parse, eval } from 'expression-eval';
// CommonJS
const { parse, eval } = require('expression-eval');
// UMD / standalone script
const { parse, eval } = window.expressionEval;

API

Parsing

import { parse } from 'expression-eval';
const ast = parse('1 + foo');

The result of the parse is an AST (abstract syntax tree), like:

{
  "type": "BinaryExpression",
  "operator": "+",
  "left": {
    "type": "Literal",
    "value": 1,
    "raw": "1"
  },
  "right": {
    "type": "Identifier",
    "name": "foo"
  }
}

Evaluation

import { parse, eval } from 'expression-eval';
const ast = parse('a + b / c'); // abstract syntax tree (AST)
const value = eval(ast, {a: 2, b: 2, c: 5}); // 2.4

Alternatively, use evalAsync for asynchronous evaluation.

Compilation

import { compile } from 'expression-eval';
const fn = compile('foo.bar + 10');
fn({foo: {bar: 'baz'}}); // 'baz10'

Alternatively, use compileAsync for asynchronous compilation.

Security

Although this package does avoid the use of eval(), it cannot guarantee that user-provided expressions, or user-provided inputs to evaluation, will not modify the state or behavior of your application. This library does not attempt to provide a secure sandbox for evaluation. Evaluation of arbitrary user inputs (expressions or values) may lead to unsafe behavior. If your project requires a secure sandbox, consider alternatives such as vm2.

License

MIT License.