array.md

Array

• Array.from
• Array.of
• [].fill
• indexOf with tilde
• Array truncation

array-from

It converts any data structures that implement Iterator interface to array. Iterable data structures include:

• Array
• String
• Map
• Set
• arguments
• DOM data structures Please note WeakMap, WeakSet and plain object are not iterable.

Array.from('hello'); // ['h', 'e', 'l', 'l', 'o']
Array.from([1, 2, 3]); // [1, 2, 3]

Array.from([1, 2, 3], x => x + x); // [2, 4, 6]
Array.from({length: 5}, (v, i) => i); // [0, 1, 2, 3, 4]

const s = new Set();

[2, 3, 5, 4, 5, 2, 2].forEach(x => s.add(x));

Array.isArray(s); // false
Array.isArray(Array.from(s)); // true

Array.from(arguments) // gives you the array

array-of

It's used to create an array in a consistent way (no function overriding).

// old way
Array() // []
Array(3) // [, , ,] empty slots not undefined
Array.from({length: 3}) // [undefined, undefined, undefined]
Array(3, 11, 8) // [3, 11, 8]

// new way
Array.of(3, 11, 8) // [3, 11, 8]
Array.of(3) // [3]
Array.of() // []

array-fill

['a', 'b', 'c'].fill(7) // [7, 7, 7]

['a', 'b', 'c'].fill(7, 1, 2) // ['a', 7, 'c']
// 2nd arg - start index
// 3nd arg - end index exclusive

indexof-tilde

~-1 is 0. ~x is equal to -(x+1).

if (~[1, 2].indexOf(1)) {
  // if array has element 1 dosomething 
}

Array Truncation

// from end
[1,2,3,4,5].slice(-3); // [2,3,4]
[1,2,3,4,5].slice(-1); // [5]

// from start
var array = [11, 12, 13, 14, 15];  

array.length = 3;  
console.log(array); // [11,12,13]

array.length = 0;  
console.log(array); // []