Expression Helpers

AMPATH Forms provide expression helpers that are useful for computing common domain-specific calculations.

Here's a link to the expression helpers implementation (opens in a new tab). You can add your own custom expression helpers to this file to make them available in the Form Builder.

Below is a reference of the functions currently available.

arrayContains

arrayContains(array, members)

Parameters

• array: An array of values, typically concept UUIDs.
• members: A value for which you want to assert its presence in the source array.

Return value

A boolean. Returns true if members is an empty array. If members is not an array, it returns true if members is not contained in the array. If members is an array, this function returns true if all of the elements in members are contained in the source array as well - and if otherwise, returns false.

Example

Here's a set of questions from the Client Enrollment section of a VDot Enrollment form.

{
  "label": "Reason for referral",
  "type": "obs",
  "id": "referralReason",
  "questionOptions": {
    "concept": "1887AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
    "rendering": "multiCheckbox",
    "answers": [
      {
        "concept": "164075AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
        "label": "Sub optimal adherence"
      },
      {
        "concept": "64132ecd-3a0f-41b8-b743-78c26af2f4b9",
        "label": "Newly initiating ART"
      },
      {
        "concept": "5619AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
        "label": "Unstable Caregiver"
      },
      {
        "concept": "989AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
        "label": "Age 0-4 years"
      },
      {
        "concept": "5622AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
        "label": "Other"
      }
    ]
  }
},
{
  "label": "Specify other reason",
  "type": "obs",
  "id": "otherReferralReason",
  "questionOptions": {
    "concept": "160632AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
    "rendering": "text"
  },
  "validators": []
}

We want to validate the Specify other reason question so that it only gets displayed when Other is chosen amongst the answers to the preceding question.

To achieve this, add the following hide expression to the Specify other reason question definition:

"hide": {
  "hideWhenExpression": "isEmpty(referralReason) || !arrayContains(referralReason,'5622AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA')"
}

This expression essentially says:

• Hide the Specify other reason question if the preceding question did not get answered. This is what the first part of the expression isEmpty(referralReason) does.
• Hide the Specify other reason question if Other is not selected amongst the answers to the preceding question.

arrayContainsAny

Tests whether the source array contains members (or the values contained in members if it is an Array). Returns true if members is/are in array, and false otherwise.

arrayContainsAny(array, members)

Parameters

• array: array
• members: an array or any value

Return value

A boolean. Returns true if members is/are in array, and false otherwise.

calcBSA

Computes a total body surface area (BSA) given a valid height and weight value.

calcBSA(height, weight)

Parameters

• height: number
• weight: number

Return value

A number if height and weight values are provided. Otherwise, returns null.

calcBMI

Computes body mass index (BMI) given a valid height and weight value.

calcBMI(height, weight)

Parameters

• height: number
• weight: number

Return value

A number if height and weight values are provided. Otherwise, returns null.

calcBMIForAgeZscore

Computes a patient's age and sex standardised BMI (BMIz) score .

calcBMIForAgeZscore(bmiForAgeRef, height, weight)

Parameters

• bmiForAgeRef
• height: number
• weight: number

Return value

A string if the height and weight values are valid and a valid bmiForAgeRef is provided. Otherwise, returns null.

calcHeightForAgeZscore

calcHeightForAgeZscore(heightForAgeRef, height, weight)

Parameters

• heightForAgeRef
• height: number
• weight: number

Return value

A string if the height and weight values are valid and a valid heightForAgeRef is provided. Otherwise, returns null.

calcWeightForHeightZscore

calcWeightForHeightZscore(weightForHeightRef, height, weight)

Parameters

• weightForHeightRef
• height: number
• weight: number

Return value

A string if the height and weight values are valid and a valid weightForHeightRef is provided. Otherwise, returns null.

extractRepeatingGroupValues

extractRepeatingGroupValues(key, array)

Parameters

• key: any
• array: Array

Return value

formatDate

formatDate(value, format, offset)

Parameters

• value: Date or any
• format: string
• offset: string

Return value

A Date object. If value is not a valid Date, returns a new Date from invoking new Date(value). If value is null or undefined, it throws an exception.

isEmpty

isEmpty(val)

Parameters

• val: The id of the question being referenced.

Return value

A boolean. Returns true if the question being referenced has an answer and false otherwise.