expression-parser

Resolves templated expressions in a secure local scope.

resolveExpression function

Arguments:

• expression: expression templated string
• context (optional): context from where to resolve expressions
• options (optional): parser options:
  • passContextToEmptyFunctions?: boolean (default true): Allow to pass the context object into empty functions calls in single expression strings. Anonymous functions are not supported
  • transformArrayNegativeIndex?: boolean (default true): Allow and parse negative indexes correctly

Example:

import { resolveExpression } from '@aircall/expression-parser'

const template = 'Start: ${variable.start}, End ${variable.end}'
const context = {
  start: '09:00',
  end: '12:00',
}

resolveExpression(template, context);
// returns 'Start: 09:00, End 12:00'

There are some use cases in the E2E tests

Default expression handling

Default expressions come in the form of ${<JavaScript code to evaluate>}. The templates are delimited with ${ and } strings and all the JavaScript code inside will be evaluated. If there is more than one expression or there is some text around the template, it will return a string evaluating all of them.

For example, with this context:

{
  content: {
    input: 2,
    id: 'operation',
    executionId: 1234,
  },
  environment: {
    variables: {
      input: 1,
      inputArray: [1, 2, 3],
      inputObject: {
        'spaced name': 'name'
      },
      getInput: (context) => {
        return context.environment.variables.input;
      },
      isBelow: (a, b) => a < b,
    commonVariablePrefix: "a",
    current: 2,
  },
}

The following expressions are supported:

| Template | Result | More information | | ---------------------------------------------------------- | -------------------------------------- | ------------------------------------------------------------------------------- | | ${environment.variables.input} | 1 | | | ${environment.variables.inputArray[0]} | 1 | resolves to first item of the variable input array | | ${environment.variables.inputArray[-1]} | 3 | resolves to last item of the variable input array | | ${environment.variables.inputObject['spaced name']} | 'name' | resolves to the variable input object property spaced name | | ${environment.services.getInput()} | 1 | executes the service function getInput with the context passed as an argument | | ${environment.services.getInput} | Function getInput() | returns the service function | | ${environment.services.isBelow(content.input,2)} | false | executes the service function isBelow with content.input value and 2 | | I, ${content.id}, execute with id ${content.executionId} | 'I, operation, execute with id 1234' | formats a string getting content object values | | ${true} | true | | | ${false} | false | | | ${null} | null | | | ${undefined} | undefined | | | ${<number>} | <number> | returns the number passed | | ${() => {}} | () => {} | returns the lambda function |

It is possible to nest multiple expressions if you write them in proper JavaScript code. For example:

Given this context:

{
  environment: {
    variables: {
      a1: (v) => `method a1: ${v}`,
      a2: (v) => `method a2: ${v}`,
      a3: (v) => `method a3: ${v}`,
    },
    commonVariablePrefix: "a",
    current: 2,
  },
};

The expression

 ${environment.variables[`${environment.commonVariablePrefix}${environment.current}`]}

returns the function:

(v) => `method a2: ${v}`