JavaScript Fundamentals - Part 2

Activate Strict Mode

Strict mode creates visible errors in developer console, where in other situations without strict mode the code will fail silently.

Function Declaration vs. Expression

Declaration

function f1 (birthYear){
    return 2021 - birthYear;
}

Can call the function before the it is defined.

Expression

const f2 = function (birthYear){
    return 2021 - birthYear;
}

Cannot access the function before it is defined.

Arrow Function

For simple one-line function:

const f3 = birthYear => 2021 - birthYear;

For multi-line function:

const yearRetire = (birthYear, firstName) => {
    const age = 2021 - birthYear;
    const retire = 65 - age;
    return `${firstName} retires on ${retire} years`;
}

Array Operations

Unshift

['Micheal', 'Steven'] —> ['John', 'Micheal', 'Steven']

friends.unshift('John')

push

['Micheal', 'Steven'] —> [ 'Micheal', 'Steven', 'John']

const newLength = friends.push('John')

Returns the length of the new Array.

pop & shift

pop - pop the last one
shift - pop the first one

indexOf

If exist - return the index
If not exist - return -1

includes

Strict Mode!!

return a boolean value whether the element exists in the array

Objects

console.log(`jonas has ${jonas.friends.length} and his best friend is ${jonas.friends[0]}`)

Object Methods

const jonas = {
    birthYear: 1991,
    friends: ['Micheal', 'Peter', 'Steven'],
    calcAge: function () {
        return 2021 - this.birthYear;
    }
};

console.log(jonas.calcAge());
// this refers to the object that is calling the method