Syntax

3 min read, 489 words syntaxjavascriptlanguagegrammerclosure

Loop

loop syntax	description
for ... in	loop through objects
for ... of .forEach()	loop through array
[1,2].map(n => n+1)	Array Methods, run a fn on each array item

• Asynchronous Programming - Non deterministic programming
• In JavaScript, a variable can be declared after it has been used. Hoisting
  • Variables defined with let and const are hoisted to the top of the block, but not initialized.
  • Meaning: The block of code is aware of the variable, but it cannot be used until it has been declared.
  • JavaScript only hoists declarations, not initializations.

Difference between javascript function and assigning function to a variable?

Both are different. Source (opens new window)

var functionOne = function() {
// Some code
};

function functionTwo() {
// Some code
}

• Variant #2 uses hoisting, whereas #1 would be initalized only once variable is reached and read by compiler.
• variant #1 uses anonymous function (opens new window) assigned to a variable.

Tagged Template Literals Use cases

• static content and dynamic content
• just tagged templated string in jest to parameterized test cases. test.each
• change data to human redable strings 2 hours ago
• calculate the works in template and calculate read time count.
• Localization
• GraphQL

const fb: string = "facebook";
const inst: string = "instagram";
// const x: string | null | undefined | '' = 'http:xing'
const x: string | null | undefined | "" = null;

// its horibble
const text = `
facebook  = ${fb}
${x}
${x ? x : ""}
${x ? x : null}
${x && x}
${x ?? x}
instagram = ${inst}
`;

console.log(text);

Javascript Closures

var num = 4;
function outer() {
  var num = 2;
  function inner() {
    num++;
    var num = 3;
    console.log(num);
  }
  inner();
}
outer(); // 3

Arrays

• How to add and remove from start and end of array? push, pop, unshift, shift
• Test if item in array array.includes(item)

JSON and Objects

javascript can parse JSON (string) easily, Objects require more tokenization parsing processing

Modules System

commonJS, UMD, AMD, ES6 Modules

import * as React from "react";
const { useState } = React;

Diff b/w == and ===

operator	description
==	checks only values
===	checks both type and value

1 == "1" ? console.log("T") : console.log("F");
1 === "1" ? console.log("T") : console.log("F");

Variable Arguments, Parametric Polymorphism

function variableArguments(...args: any[]) {
  console.log(args.length);
  console.log(...args);
}
variableArguments("hello", "how", "are", "yo", 4, 3, 2);

Subscribe to our Newsletter

If you like my work and think it was helpful kindly support my work