Flatten array

flatten.js

/**
 * Recursively flatten an array.
 * @example
 *  input:   [[1,2,[3]],4]
 *  output:  [1,2,3,4]
 **/
function flatten(current) {
    let accumulator = []    
    if (Array.isArray(current)) {
        // Process the nested array.
        current.forEach(item => {
            // Flatten this children and add it to the result.
            accumulator = accumulator.concat(flatten(item))
        })
    } else {
        // No need for further processing.
        accumulator.push(current)
    }
    return accumulator
}

module.exports = flatten