Javascript Cheatsheet

let variable-name; // Just declaration
let variable-name = value; // declaring variable and assigning it with some value
let var1 = value1, var2 = value2, var3 = value3; // multiple variables declaration with their assigned values

<script type="text/javascript">  ...
</script>

<script src="filename.js"></script>

console.log("hello");       // to display message to the browser console
document.write(x);    // to write to HTML
prompt("Your name?","friend");    // input dialog. Second argument is the initial value
alert(x); // writes in an alert box

"use strict";  // throw errors for some of javascript silent errors and tells browser to be more strict.

let age = 20; 

if (age > 18) {
  console.log('Adult');
}

let age=7;

if(age<0) {
console.log('invalid age');
} else if (age<5 && age >0) {
console.log('Infant');
} else if (age>=5 && age<=18) {
  console.log('child');
} else if (age>18) {
  console.log("Adult");
}

// what is hello in different languages
let language = "italian";
switch(language){
  case "french" :
    console.log('BONJOUR');
    break;
  
  case "spanish":
    console.log('Hola');
    break;
  
  case "hindi" :
    console.log("Namaste");
    break;
  
  default:
    console.log('Hello');
}

console.log('simple for loop');
for(let i=1;i<=10;i++) {
  console.log(i);
}

let info = {
  name: "foo",
  id: 123
}

for (let x in info) {
  console.log(x); <em>// prints keys of info which are name and id</em>
}

let mobiles = [ "iPhone", "Samsung", "OnePlus", "Pixel"];
for(let mbl of mobiles) {  
    console.log(mbl);
} 

let i=1;
while(i<=10) {
  console.log(i);
  i++;
}

let i=1;
do {
  console.log(i);
  i++;
} while(i<=10);

let arrayName = [value1, value2,..etc];
// or
let arrayName = new Array("value1","value2",..etc);

// declaring a function
function function-name(parameters){ // here parameters are optional
    //code
}
function-name(parameters); // calling a function

(argument-list) => expression

let sum= (a,b,c) => {
    return a+b+c;
}
console.log(sum(10,20,30));

let promise = new Promise(function(resolve, reject){
    //code
}); 

async function functioname(parameters){
	//code
}

async getTodos(userObj){
	const res = await fetch([url]);
	const data = await res.json()    
	return data;
}

let data = await getTodos({fn: "foo"});

try {
    //code
} catch(err) {
    //code
}

throw "Error message";    // throw error text to user

/pattern/modifiers;