How to validate fields in lightning component in Salesforce?

Hi Nikita,

Here is the example

<aura:component >
<center>
<br/>
<h5> <b> Age Validator </b> </h5> <br/>
Enter your age: <ui:inputNumber aura:id="inputCmp"/> <br/>
<ui:button label="Submit" press="{!c.validateAge}"/>
</center>
</aura:component>

{
validateAge : function(component) {
var ageField = component.find("inputCmp");
var ageValue = ageField.get("v.value");

if(isNaN(ageValue) || ageValue == '')
{
ageField.set("v.errors", [{message:"Enter a valid age."}]);
}
else if(parseInt(ageValue) > 150)
{
ageField.set("v.errors", [{message:"This is not a valid age."}]);
}
else if(parseInt(ageValue) < 18)
{
ageField.set("v.errors", [{message:"Minimum age to submit this form should be greater or equal 18"}]);
}
else
{
ageField.set("v.errors", null);
}
}
}