SOURCE

function getType(val) {
    if (val === null) {
        return null
    }
    if (typeof val === 'object') {
        let valClass = Object.prototype.toString.call(val)
        return valClass.slice(7, valClass.length - 1)
    } else {
        return typeof val
    }
}

console.log(getType(123))
console.log(getType('123'))
console.log(getType(null))
console.log(getType([1, 2, 3]))