When I develop with Javascript, I have a few things that are not certain. For my reference, I organize them here.

=== vs ==

=== operator compares a value with another value. It validates the type of value and the value together. So it's stricter than ==.

But the one thing that you should remember is the operator === can be used for string and number type only.

let vs var

Using let is more recommended than using var. It's stricter. In other words, it helps you to avoid causing an error.

A variable declared by let is limited to a block in which the variable is placed.

function a() {
	let v = ‘test’;
	console.log(v);
}
console.log(v); // This causes an error.

Primitive types

Javascript has boolean, number, string, undefined, object, function, and symbol as primitive types.

let isBool = false;
typeof isBool; // boolean

let age = 30;
typeof age; // number

let name = “woong”;
typeof name; // string

let icecreams = [“choco”, “vani”, “lemon”, “strawberry”];
typeof icecreams; // object

let isNull = null;
typeof isNull; // object

let fa = function() { console.log(“function”); }
typeof fa; // function

let isUndefined;
typeof isUndefined; // undefined