JavaScript built-in functions

JavaScript has ready-made functions that come with the language; we will go through a few of them here:

Functions for objects

Object.freeze()

Using freeze() will ensure that an object and its properties become read-only:

const myObject = { 
    myProp1: 2, 
    myProp2: "my value" 
};

Object.freeze(myObject);

myObject.myProp1 = 3; 
myObject.myProp2 = "this won't become the value"
// myObject and its properties won't change

However, if a property contains a (nested) object, then that property can still change:

const myObject = { 
    myProp1: 2, 
    myProp2: { 
        myNestedProp: "my value" 
    }
};
Object.freeze(myObject);

myObject.myProp2.myNestedProp = "your value"; 
// the program will acknowledge this change to myNestedProp

Objects for arrays

every()

The every() method determines if all elements in an Array type meet a specific condition:

const myArray = [1, 3, 9, 23, -5]
const yourArray = [2, 3, 4, 5]

// condition
const isPositive = (number) 
    => number > 0

myArray.every(isPositive) 
// false

yourArray.every(isPositive)
// true