mathjs/src/expression/transform/utils/compileInlineExpression.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

import { isSymbolNode } from '../../../utils/is'

/**
 * Compile an inline expression like "x > 0"
 * @param {Node} expression
 * @param {Object} math
 * @param {Object} scope
 * @return {function} Returns a function with one argument which fills in the
 *                    undefined variable (like "x") and evaluates the expression
 */
export function compileInlineExpression (expression, math, scope) {
  // find an undefined symbol
  const symbol = expression.filter(function (node) {
    return isSymbolNode(node) &&
        !(node.name in math) &&
        !(node.name in scope)
  })[0]

  if (!symbol) {
    throw new Error('No undefined variable found in inline expression "' + expression + '"')
  }

  // create a test function for this equation
  const name = symbol.name // variable name
  const subScope = Object.create(scope)
  const eq = expression.compile()
  return function inlineExpression (x) {
    subScope[name] = x
    return eq.evaluate(subScope)
  }
}