Flatten - Javascript Function

flatten.js

myArray = [[1,2,[3]],4]; // -> [1,2,3,4]


function flatten(arrayVal) {
    return arrayVal.reduce((newArray, currentValue) => Array.isArray(currentValue) ? newArray.concat(flatten(currentValue)) : newArray.concat(currentValue), [])
}

console.log('flatten: ', flatten(myArray));