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JavaScript - Const

ES2015 introduced two important new JavaScript keywords: let and const. Variables defined with const behave like let variables, except they cannot be reassigned.

The keyword const is a little misleading. It does NOT define a constant value. It defines a constant reference to a value. Because of this, we cannot change constant primitive values, but we can change the properties of constant objects. If an object, you can change it's contents! 


const PI = 3.141592653589793;
PI = 3.14;      // This will give an error
PI = PI + 10;   // This will also give an error


// You can create a const object:
const car = {type:"Fiat", model:"500", color:"white"};

// You can change a property:
car.color = "red";

// You can add a property:
car.owner = "Johnson";



let resistanceMsg = "I will resist!";
const borgMsg = "Resistance is futile!";

try
{
    // This will create an error
    borgMsg = resistanceMsg;
}
catch (error)
{
    alert("you cant reassign a const - dummy!");
    console.error(error);
}

let demo1 = document.getElementById("demo1");
demo1.innerHTML = borgMsg;