Demo1

node v14.14.0
version: 0.9.3
endpointsharetweet
Null vs Undefined
//Show a variable uninitialized is set to undefined by the runtime var x; var y = 100; console.log(x); console.log(y); //When you hit run, you will notice - undefined, 100 and another undefined. Ignore the last undefined as it is the //return value of invoking console.log(...) method. So always ignore the last undefined in a console.log(...) call
Typeof operator
var name = "John"; var cost = 99.25; var salary; var str = null; function fn() { console.log("I am a function!"); } console.log(typeof(name)); console.log(typeof(cost)); console.log(typeof(salary)); console.log(typeof(str)); console.log(typeof(fn));
Floating point approximation errors
0.1 + 0.2
Dividing by zero
100/0
-99/0
String to number conversion
parseInt("100");
parseInt("hello");
Mixing concatenation operator with numbers and strings could lead to unpredicatable results
'37' + 7;
//But... '37' - 7;
Instantiating Objects
var obj1 = new Object();
var obj2 = {};
var user = { first_name : "John", last_name : "Doe"};
user.age = 25;
user
Arrays
var even = new Array(); even.push(2); even.push(4); even.push(6); even;
var odd = [3, 5, 7]; odd;
Iterating over an array
var colors =["red", "blue", "green"]; for (var i = 0; i < colors.length; i++) { console.log(colors[i]); }
colors.forEach(function(color) { console.log(color); });
Equality
'2' == 2
'2' === 2
Classes
class Shape { constructor() { this.X = 0; this.Y = 0; } move(x, y) { this.X = x; this.Y = y; } distanceFromOrigin() { return Math.sqrt(this.X * this.X + this.Y * this.Y); } } const s = new Shape(); s.move(10, 10); console.log("Distance from origin ", s.distanceFromOrigin()); //Interestingly if you look at the type of Shape it would not say class and instead function - so classes are behind //the scenes are still implemented as Constructor functions typeof(Shape)
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