Sample Function Call in React in Line 15

import React { Component } from 'react';

class Cobol extends Component{
	state = {
		numOfTimesHeSaidCobolIsGreat: 1
	};
	
	render(){
		return (
			<div>
				<span>{this.cobolIsTheBestThingEver()}</span>
				<button>BestProgLang</button
			</div>
		);
	}
	function cobolIsTheBestThingEver(){
		const { numOfTimesHeSaidCobolIsGreat } = this.state;
		return count === 0 ? "Pascal" : numOfTimesHeSaidCobolIsGreat;
	}
}	

export default Cobol;

Function In JS Structure

function functionName(param1, param2, etc..){
	//func logic goes here
}

CallBack Function

• A function that is a parameter of another function
• The inner function is called as soon I invoke the outer function

const successfullyListeningTo = (nameOfSinger) => {
	console.log(`You are successfully listening to ${nameOfSinger}!`);
}

const listenToSinger = (callbackfunc) => {
	const singer = 'Sting'
	callbackfunc(singer);
}


successfullyListeningTo(listenToSinger);

//You are successfully listening to Sting

Arrow Functions

Function without Arrow Function

coolfunc = function(){
	return "This is a cool function!";
}

Arrow Function

coolfunc = () => {
	return "This is a cool Arrow Function!";
}

• If the function has one statement I can omit:

  • the return statement
  • the curly braces

coolfunc = () => "This is a cool Arrow Function!";

Arrow Function With Parameters

coolfunc = (myval) => {
	return "Hi there " + myval;
}

• IF the Arrow function has only one parameter I can omit:
  • the parentheses
  • the return statement

coolfunc = myval => "Hi there " + myval;

Important Functions

1. alert() function: outputs data in an alert box in a window
2. confirm() function: opens a yes/no option dialog box and returns a boolean value depending on the user click
3. console.log() function: writes stuff to the browser console
4. document.write() function: writes stuff directly to the HTML doc
5. prompt(): creates a dialogue for user input

Array Methods

1. concat(): join several arrs into one
2. indexOf(): Search the array for the specified element if found return its position else return -1
3. join(): combines the elements into a single string and returns that string
4. lastIndexOf(): outputs the last position at which a given element exists in the array
5. pop(): removes the last element within the array
6. push(): add a new element to the end of the array
7. replace(): Replace a specified value with another value in the String
8. reverse(): reverse the order of the items in the array
9. search(): search the string for the specified value and position of the match
10. shift(): remove the first item in the array
11. slice(): pulls a copy of a portion of the array into a new arr
12. sort(): sort the items in the array alphabetically
13. splice(): adds elements in a specific way and position
14. toString(): converts the element to Strings aka the renowed Java must know method
15. unshift(): adds a new element to the array at the beginning

Variables In JS

1. var: cannot be reassigned
2. const: cannot be reassigned and cannot be used before they are declared
3. let: can be reassigned but not redeclared

5 Must Know Functions

1. ... : Spread operator expands an array into its elements
2. filter(): Filter method creates a new array and fills it up with the elements that meet a certain condition
3. map(): similar to filter but is used to modify elements instead
4. reduce(): transform the array into something else i.e. reduce the array into one value
5. includes(): check if a specified string exists within the array

String Methods In JS

To String...Return A String In Relation To The Specified Obj

const myArr = [2,4,6,"b","c"];
let myNum = 6;
console.log(myArr.toString()); //Prints "2,4,6,b,c"
console.log(myNum.toString()); //Print "6"

Join: Returns a new String by Concatenating All El in The Arr

const myArr = ["Grand Theft Auto","True Crime","PUBG","COD","Saints Row"];
let myNum = 6;
console.log(myArr.join()); //Prints       Grand Theft Auto, True Crime, PUBG,COD, Saints Row
console.log(myArr.join(" ")); //Prints    Grand Theft Auto True Crime PUBG COD Saints Row
console.log(myArr.join("-")); //Prints    Grand Theft Auto-True Crime-PUBG-COD-Saints Row