TypedArray.from

TypedArray.from(source[, mapFn[, thisArg]])

where TypedArray is one of:

Int8Array
Uint8Array
Uint8ClampedArray
Int16Array
Uint16Array
Int32Array
Uint32Array
Float32Array
Float64Array

// Set (iterable object)
var s = new Set([1, 2, 3]);
Uint8Array.from(s);
// Uint8Array [ 1, 2, 3 ]


// String
Int16Array.from('123');                      
// Int16Array [ 1, 2, 3 ]


// Using an arrow function as the map function to
// manipulate the elements
Float32Array.from([1, 2, 3], x => x + x);      
// Float32Array [ 2, 4, 6 ]


// Generate a sequence of numbers
Uint8Array.from({length: 5}, (v, k) => k);    
// Uint8Array [ 0, 1, 2, 3, 4 ]

if (!Int8Array.__proto__.from) {
    (function () {
        Int8Array.__proto__.from = function (obj, func, thisObj) {

            var typedArrayClass = Int8Array.__proto__;
            if(typeof this !== 'function') {
                throw new TypeError('# is not a constructor');
            }
            if (this.__proto__ !== typedArrayClass) {
                throw new TypeError('this is not a typed array.');
            }
 
            func = func || function (elem) {
                    return elem;
                };

            if (typeof func !== 'function') {
                throw new TypeError('specified argument is not a function');
            }

            obj = Object(obj);
            if (!obj['length']) {
                return new this(0);
            }
            var copy_data = [];
            for(var i = 0; i < obj.length; i++) {
                copy_data.push(obj[i]);
            }

            copy_data = copy_data.map(func, thisObj);

            var typed_array = new this(copy_data.length);
            for(var i = 0; i < typed_array.length; i++) {
                typed_array[i] = copy_data[i];
            }
            return typed_array;
        }
    })();
}