app.contact is the instance of Contact API, which provide functions to access Contacts from your app. In order to use this API, you need to add these permissions to you package.json file.
android.permission.READ_CONTACTS
android.permission.WRITE_CONTACTS
A working example of Contact API
var contacts = app.contact.getAll();
console.log(contacts);
app.contact.getAll()Returns Array of JSON Objects with details of all available contacts in user's phone.
An example of above code:
let contacts = app.contact.getAll();
contacts.forEach(function(contact){
    console.log(contact.name, contact.phone_number, contact.email);
})
app.contact.add(name, number, email)name String
    name by which you want to add contact.number String
    number which you want to add into contact.email String
    email which you want to add into contact (email is optional).Add the given contact details into user's phone.
NOTE: It returns a JSON Object, {error: true/false, msg: 'error msg'}  
if contact add successfully then error will be false otherwise true.
An example of above code:
let name = 'alex';
let number = '123457896'
let email = 'example@androidjs.com'
let status = app.contact.add(name, number, email);
if(!status.error){
    console.log('contact added to phone');
}else{
    console.log(status.error, status.msg);
}
app.contact.getByName(name)name String
    name which you want to search.NOTE: returns JSON Object of uesr's details if record found otherwise error object
Search contact details of given name .
An example of above code:
let name = "alex"
let status = app.contact.getByName(name);
if(status.error == undefined){
    console.log(status.name, status.phone_number, status.email);
}else{
    console.log(status.error, status.msg);
}
app.contact.getCount()Returns the total number of contacts saved in user’s phone.
An example of above code:
let count = app.contact.getCount();
console.log(count);