Apex: Get number of contacts for a list of accounts

Map<Id, Account> accountsById = new Map<Id, Account>([SELECT Id, Name FROM Account LIMIT 10]);
Set<Id> accountIds = accountsById.keySet();

Map<Id, Integer> numberOfContacts = new Map<Id, Integer>();
for (Account acc : [SELECT Id, Name, (SELECT Id FROM Contacts) FROM Account WHERE Id IN :accountIds]) {
    numberOfContacts.put(acc.Id, acc.Contacts.size());
}
System.debug(numberOfContacts);

Apex: Get all required fields of an sObject

Map<String, Schema.SObjectType> m  = Schema.getGlobalDescribe();
Schema.SObjectType s = m.get('Contact');
Schema.DescribeSObjectResult r = s.getDescribe();
Map<String,Schema.SObjectField> fields = r.fields.getMap();

for(String field : fields.keyset()) {
    Schema.DescribeFieldResult describeResult = fields.get(field).getDescribe();
    if (describeResult.isCreateable()  && !describeResult.isNillable() && !describeResult.isDefaultedOnCreate()) {
        System.debug(field);
    }
}

REST API Response Codes

Apex: Monitor / manage heap during execution

Use the code below in your Apex code to monitor the heap during execution.

System.debug(LoggingLevel.Debug, 'Heap Size: ' + Limits.getHeapSize() + '/' + Limits.getLimitHeapSize());

Reference: https://help.salesforce.com/articleView?id=000170956&type=1

Javascript: Pattern to create instance-specific private data

To make a property private, just make it local to the constructor. Any outside code trying to access age variable will result in an undefined. But the outside code can still call the property that accesses this private variable using the public function getAge.

function Person(name) {

   // Define a variable only accessible inside of the Person constructor
   var age = 25;

   this.name = name;

   this.getAge = function() {
      return age;
   };

   this.growOlder = function() {
      age++;
   };
}

var person = new Person("Nicholas");

console.log(person.name);     // "Nicholas"
console.log(person.getAge()); // 25

person.age = 100;
console.log(person.getAge()); // 25

person.growOlder();
console.log(person.getAge()); // 26