dalkegama

const arrayOneLevelDeep  = [6,9,[6],6];

[].concat(...arrayOneLevelDeep);
// or
[].concat.apply([],arrayOneLevelDeep);

// Returns
[6, 9, 6, 6]

dalkegama

const someArray = [1, 2, , , [3, 4, [5, null, ["", 8, [undefined, 10]]]]];

someArray.flat(Infinity).filter(Boolean).map(Number);
// or 
someArray.toString().split(",").filter(Boolean).map(Number);

// Both returns
[1, 2, 3, 4, 5, 8, 10]

dalkegama

const someArray = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];

// toString()
someArray.toString().split(",").map(Number);

// or you could use template literal which is faster than toString()
`${someArray}`.split(",").map(Number);

// Returns
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

dalkegama

const arrayWithEmptySlots = [1, 2, , 3, , 4].flat();

//Returns
[1, 2, 3, 4]

dalkegama

const someArray = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];

someArray.flat(Infinity);

// Returns 
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

dalkegama

const monkeys =["🙈",["🙉","🙊"],"🐒"].flat();
// one above is same as the one below
const monkeys = ["🙈",["🙉","🙊"],"🐒"].flat(1);

// Returns
[🙈,🙉,🙊,🐒]

dalkegama

// Long way
if(array.indexOf(item) > -1) // Item found
if(array.indexOf(item) === -1) // Item NOT found

 
// Shorthand way 👍🏽
if(array.includes(item))// Item found
if(!array.includes(item))// Item NOT found
 
if(~arr.indexOf(item)) // Item found

dalkegama

let someString = "doubt-not";

someString = "false";
!!someString // returns true

someString = "0"; 
!!someString //returns true

let someString = undefined; 
!!someString //returns false

dalkegama

// Use this:
Boolean(someString); // returns true, same as !!someString
Boolean("0"); //returns true, in JavaScript, a non-empty string is always true.


//Not this:
const foo = new Boolean(bar); // returns a wrapper object

dalkegama

Number(someStringNum) + 2;  // returns 5.5
Number(null);  // returns 0
Number("");    // return NaN


// Fast but messy
someStringNum * 1 + 2;  // returns 5.5