chaining

// Array.prototype = {

//     left: num => x.slice(num),
//     divideBy: x => x.map(y => y / num),
//     value: x => x

// }

let t1 = [
    {name: 'Alice', age: 20},
    {name: 'Bob', age: 30},
    {name: 'Harry', age: 40},
    {name: 'Jerry', age: 50}
]

function Utils(x) {
    if(!(this instanceof Utils)){
        console.log("Here")
        return new Utils(x)
    }
    this.value = Array.isArray(x) ? x : [x]
    return this
}

Utils.prototype.map = function(f){
    this.value = this.value.map(y => f(y))
    return this
}
Utils.prototype.take = function(n){
    this.value = this.value.slice(0, n)
    return this
}
Utils.prototype.divideBy = function(n){
    this.value = this.value.map(y => y / n)
    return this
}

Utils.prototype.fold = function(){
    return this.value
}

let res = Utils(t1).map(y => y.age).take(3).divideBy(10).fold()