Checking if rendered lightning:input components are populated

Question

I am building a Lightning Component form with sections. I want to display a big check mark icon on the section if all the rendered lightning:input fields are filled out.

I have successfully tested this approach:

Markup:

<lightning:input aura:id="fieldId" type="number" name="input1" required="true" 
    label="Enter a number" />
<lightning:input aura:id="fieldId" type="number" name="input2" required="true" 
    label="Enter another number" />
<lightning:button variant="brand" label="Check" value="check" 
    onclick="{!c.testMe}"/>

Controller:

testMe : function(component) {

    var allComplete = component.find('fieldId').reduce(function (validSoFar, inputCmp) {
        return validSoFar && !inputCmp.get('v.validity').valueMissing;
    }, true); 
    if (allComplete) {
        console.log('All fields complete!');
    } else {
        console.log('Some fields are missing values.');
    }
},

The problem arises when I start making the form dynamic using aura:if to conditionally hide lightning:input fields.

If I change my markup to this, the function fails and nothing shows up in the console:

<lightning:input aura:id="fieldId" type="number" name="input1" required="true" label="Enter a number" />
<aura:if isTrue="{! false }">
    <lightning:input aura:id="fieldId" type="number" name="input2" required="true" label="Enter another number" />
</aura:if>
<lightning:button variant="brand" label="Check" value="check" onclick="{!c.testMe}"/>

---

Based on the helpful answer from itzmukeshy7, here is my revised, working controller function:

testMe : function(component) {

    var rows = component.find('fieldId');

    // The following row handles all return types for the find function: 
    // 1. A component
    // 2. An array of components, or 
    // 3. Undefined (no matching components)
    var elements = [].concat(rows || []);

    var allComplete = elements.reduce(function (validSoFar, inputCmp) {
        return validSoFar && !inputCmp.get('v.validity').valueMissing;
    }, true);

    if (allComplete) {
        console.log('All fields complete!');
    } else {
        console.log('Some fields are missing values.');
    }

},

Answer 1

This is all fine, there is a trick which is very much hidden in the documentation:

Here is what the documentation says:

So we can handle this with concat method of array:

var rows = c.find('rowSelector');
var elements = [].concat(rows || []);
/* Now here the elements will always be an array, and won't break your code anymore. */

Answer 2

When running your example, I'm getting an error saying reduce is not a valid function. You can enable debug mode for lightning components to get these errors.

The reason for this is your component.find(...) method. Component.find has two return types. Either an Object or Object[].

In the first example you have multiple instances of a component with id "fieldId". Thus the return type will be a list of aura components.

In the second example there is only one aura component as the other one is conditionally rendered. Hence only one component with id "fieldId" is found. Component.find will return a single object and not a array of objects.

You can resolve the issue by first checking if the result of component.find is an array. If not then add it to an array and apply the same reduce method for simplicity sake.