[ES6] 22. Const

‘const‘ keyword is for creating a read only variable, something you can never change once created.

‘const‘ likes ‘let‘ keyword alos has block scope.

describe("using const", function(){

    it("will make a variable read-only", function(){

        const MAX_SIZE = 10;

        //MAX_SIZE = 12; //SyntaxError

        expect(MAX_SIZE).toBe(10);  //true
    });

    it("can shadow outer declaration", function(){

        const x = 12;
        var doWork = function(){

            let x = 10;
            return x;
        };

        var result = doWork();
        expect(result).toBe(10);  //true
        expect(x).toBe(12); //true
    });

    it("const also has block scope", function(){

        if(true){
            const x = 12;  //SyntaxError, x is not defined
        }

        var doWork = function(){

            let x = 10;
            return x;
        };

        var result = doWork();
        expect(result).toBe(10);  //true
        expect(x).toBe(12); //true
    });
});