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Data Types

This section will cover code samples for all the primitives that are available within Javascript.

Var, Let and Const

This sections will shows differences between var, let and const. var is function scoped, not blocked scoped like let and const

if (true)  {
    var name = 'jon';
}
console.log(name);

var is function scoped

try {
    const example = function() {
        var scoped = 'test';
    };
;
    console.log(scoped)

} catch(e) {
    console.log('This will be triggered, as var is function scoped');
}

var will allow me to redefine cars, this is not a good idea and leads to confusing-code

var testThree = 'test';
var testThree = 'test';

// var delations get hosited to the top
// When this code runs it wont throw an exception
console.log(withVar);
var withVar;

// let does not get hoisted
try {
    console.log(withLet);
    let withLet ;
} catch(e) {
    console.log('This will throw as expeceted');
}

Strings

const name = 'jon   ';
console.log('Original String = ' + name);
console.log();
console.log('Length = ' + name.length);
console.log('Uppercase = ' + name.toUpperCase());
console.log('Lowercase = ' + name.toLowerCase());
console.log('Include(\'jon\') = ' + name.includes(name));
console.log('Finding a String using indexOf(\'on\') = ' + name.indexOf("on"));
console.log('Searching a String using search(\'jon\') = ' + name.search("jon"));
console.log('Slicing first character = ',name.slice(0, 1));
console.log('Sibstring = ', name.substring(1, 3));
console.log('Replace = ', name.replace('on', 'this part has been replaced'));
console.log('Trim = ', name.trim());
console.log('Concat = ', name.concat(name));
console.log('CharAt(2) = ', name.charAt(2));
console.log('Char[0] = ', name[0]);
console.log('Split(o) = ', name.split('o'));
console.log();

Template Strings/String Interpolation

If you need to combine string your code will be easier to read when you use template strings

Template string

console.log(`city=${city} country=${country}`);

Manually concatenating strings

console.log('city=' + city + ' country=' + country);

Resources

Booleans

True

const imTrue = true;
console.log(imTrue);

False

const imFalse = false;
console.log(imFalse);

Resources

Dates

const now = new Date();
const year = now.getFullYear();
console.log(year);
const now = new Date();
const month = now.getMonth();
console.log(month);
const now = new Date();
const dayofMonth = now.getDate();
console.log(dayofMonth);
const now = new Date();
const hour = now.getHours();
console.log(hour);
const now = new Date();
const minute = now.getMinutes();
console.log(minute);
const now = new Date();
const second = now.getSeconds();
console.log(second);
const now = new Date();
const timestamp = now.getTime();
const readDataFromString = new Date(timestamp);
console.log(readDataFromString.getFullYear());

Resources

Undefined

Javascript assigns undefined when no value is explicitly set

let implict;
console.log(implict);

You can explicitly assign undefined. Explicitly setting undefined isn't recommended, as it hides the intention of the code. If you want to explicitly set something as empty, use null

const explicit = undefined;
console.log(explicit);

Undefined functions

let myFunction = function (paramter) {

    // When no parameter is passed in, this will throw undefinied
    console.log(paramter);
}
const result = myFunction();

When no return value is provided, undefined will be thrown

console.log(result);

Examples

if (implict === undefined) {
    console.log('implict is undeinifed');
}

Resources

Null

When a variable hasn't been defined correctly, Javascript will assign it undefined If you want to explicitly set something as not being set you should use null Using null instead of undefined gives other developers a better understanding of the intention of your code

let name = null;
console.log(name);

// Example
if (name === null) {
    console.log('name is null');
}

Resources

Numbers

const number = 12343.343;

console.log('ToFixed() / round decimal place', number.toFixed(2));
console.log('Math.round()', Math.round(number));
console.log('Math.floor()', Math.floor(number));
console.log('Math.ceil()', Math.ceil(number));
console.log('Math.random()', Math.random() * (100 - 0) + 0);
const age = 12;
const dogYear = (age + 1) / 7;

console.log(dogYear);
const numberOfQuestions = 1;
const numberOfCorrectResults = 3;
const percentage = (numberOfQuestions *  100) / numberOfCorrectResults;

console.log(percentage);

Resources