I went through the lightning guide and try to learn the form controls, I got the below code which show that it validates the form fields, But would like to see more insight on

1 reduce - what this function will do

2) showHelpMessageIfInvalid - what this will do? Do we have some other methods like these? where we can see these documentation?

3) v.validity'- I don't see this is used in any of the component - Help me to get clarified.

// Show error messages if required fields are blank
    var allValid = component.find('contactField').reduce(function (validFields,
    inputCmp) {
    return validFields && inputCmp.get('v.validity').valid;
    }, true);
  • BUt using this code, give an error when the record is saved. were you able to run your component correctly ?
    – Ankuli
    Commented Jan 11, 2018 at 11:19
  • Good Question and Good answer from @RedDevil. The Salesforce documentation is very confusing. I would like very much develop one better technical reference for us in future.
    – Chiarato
    Commented Dec 17, 2020 at 4:14

1 Answer 1


1 reduce - what this function will do

The reduce() method applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.

Read here for more details:

var total = [0, 1, 2, 3].reduce(function(sum, value) {
  return sum + value;
}, 0);
// total is 6

reduce function is part of array prototype javascript object. It takes a function as input and applies that on the array and returns the output.

In this case the function does a summation of array members and returns the output.This is achieved by using reduce function which applies it on each and every member

2) showHelpMessageIfInvalid - what this will do? Do we have some other methods like these? where we can see these documentation?

This method is used by Lightning:Input tag to check for validity of input tag.

showHelpMessageIfInvalid(): Shows the help message if the form control is in an invalid state.

Lets take this input example:

   <lightning:input aura:id="field" label="Last name" placeholder="Last name" required="true" /> 

since required is marked true if user doesn't enter any value the validity object for this input control will have value as valueMissing.

The other possible values are :

badInput: Indicates that the value is invalid

patternMismatch: Indicates that the value doesn't match the specified pattern

rangeOverflow: Indicates that the value is greater than the specified max attribute

rangeUnderflow: Indicates that the value is less than the specified min attribute

stepMismatch: Indicates that the value doesn't match the specified step attribute

tooLong: Indicates that the value exceeds the specified maxlength attribute

typeMismatch: Indicates that the value doesn't match the required syntax for an email or url input type

valid: Indicates that the value is valid

valueMissing: Indicates that an empty value is provided when required attribute is set to true

when a form is submitted or field validity code is triggered. Below javascript code which is present in the same link runs and checks for validity of input components

    onClick: function (cmp, evt, helper) {
        var allValid = cmp.find('field').reduce(function (validSoFar, inputCmp) {
            return validSoFar && inputCmp.get('v.validity').valid;
         }, true);
         if (allValid) {
             alert('All form entries look valid. Ready to submit!');
         } else {
             alert('Please update the invalid form entries and try again.');

If you look at the above function reduce function is used again. just to break it down into smaller chunks to explain in detail

  1. Lets say you have 4 lightning:input components with id as 'field', component.find will return an array of 4 elements

  2. Array.reduce will run for each element and the function inputCmp.showHelpMessageIfInvalid(); will check if the element is valid if not it will show the help message and the red border to highlight the field is invalid.

  3. The third line 'return validSoFar && inputCmp.get('v.validity').valid;' is basically like an if and condition ,so in this case which is your third question(' v.validity').valid checks if the component is in a valid state. v.validity is part of every lightning:input component to check for validity of the input component. Lets say that a lightning:input is marked required and user has not entered a value when this code runs it will return false which basically means the component is not valid.

  4. The return statement will return false even if one form component of your array fails for any of the invalidity status and overall allValid variable will become false.

  5. Finally the allValid will be false and an alert message will show in UI which indicates one more lightning:input tags are in invalid state. It means they have not entered data or they have not respected the fields formatter attribute etc.

  • The Lightning:input link in the answer is no longer active. Here's a link where you can find the information RedDevil was referencing: developer.salesforce.com/docs/component-library/bundle/…
    – Arthlete
    Commented Jul 26, 2019 at 21:25
  • For better understanding you may log the current state and the component labels to the console using the snippet below: console.log(`Current Validation Status :: ${validSoFar} of the Component ${inputCmp.get("v.label")}`);
    – KaLi
    Commented Oct 24, 2020 at 1:19

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