Array Methods (ECMAScript 2015) Sample

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ECMAScript 2015 specification adds additional static methods on Array and instance methods on Array.prototype .

Array.from ( items [ , mapfn [ , thisArg ] ] ) #

The Array.from() method converts an array-like object to a true array. It takes an optional second parameter, which can be used to execute a map function on each element of the array that is being created.

Array . from ( new Set ([ 1 , 1 , 2 , 3 ])); // [1, 2, 3] Array . from ( ' hello ' ); // ["h", "e", "l", "l", "o"] Array . from ( ' hello ' , x => x . charCodeAt ( 0 )); // [104, 101, 108, 108, 111]

It comes in handy when dealing with the infamous NodeList returned by document.querySelectorAll .

var divs = document . querySelectorAll ( ' div ' ); Array . from ( divs ). forEach ( function ( node ) { console . log ( node ); });

The Array.of() method creates a new Array instance with any number of arguments, regardless of their type.

Array . of ( ' hello ' ); // ["hello"] Array . of ( 1 , 2 , 3 ); // [1, 2, 3] Array . of ( ' blink ' , 182 ); // ["blink", 182]

Array.prototype.copyWithin (target, start [ , end ] ) #

The copyWithin() method copies the sequence of array elements within the array to the position starting at target . The copy is taken from the index positions of the second and third arguments start and end . The end argument is optional and defaults to the length of the array.

[ 0 , 1 , 2 , 3 , 4 ]. copyWithin ( target = 4 , start = 0 ); // [0, 1, 2, 3, 0] [ 0 , 1 , 2 , 3 , 4 ]. copyWithin ( target = 0 , start = 2 ); // [2, 3, 4, 3, 4]

If start is negative, it will be treated as length+start where length is the length of the array. If end is negative, it will be treated as length+end . [0, 1, 2, 3, 4].copyWithin(target=0, start=3, end=4); // [3, 1, 2, 3, 4] [0, 1, 2, 3, 4].copyWithin(target=0, start=-2, end=-1); // [3, 1, 2, 3, 4]

Array.prototype.fill (value [ , start [ , end ] ] ) #

The fill() method fills all the elements of an array between an optional start index and an optional end index with a static value . The start argument defaults to 0. The end argument defaults to the length of the array.

[ 0 , 1 , 2 , 3 , 4 ]. fill ( 5 ); // [5, 5, 5, 5, 5] [ 0 , 1 , 2 , 3 , 4 ]. fill ( 5 , start = 2 ); // [0, 1, 5, 5, 5] [ 0 , 1 , 2 , 3 , 4 ]. fill ( 5 , start = 2 , end = 4 ); // [0, 1, 5, 5, 4]

Array.prototype.find ( predicate [ , thisArg ] ) #

The find() method returns a value in the array, if at least one element in the array satisfies the provided predicate function. If not, undefined is returned. find() does not mutate the array on which it is called.

function startsWithLetterA ( element , index , array ) { if ( element . startsWith ( ' a ' )) { return element ; } } var cuteNames = [ ' jeff ' , ' marc ' , ' addy ' , ' francois ' ]; cuteNames . find ( startsWithLetterA ); // "addy"

Array.prototype.findIndex ( predicate [ , thisArg ] ) #

The findIndex() method returns an index in the array, if at least one element in the array satisfies the provided predicate function. If not, -1 is returned. findIndex() does not mutate the array on which it is called.