JavaScript/ First-Class Functions

- a Function is an instance of the object type.
- a Function behaves like any other object.
- we can store functions in a variable.
- we can pass a function as an argument to another function.
- we can return a function from a function. 
=> First-Class Functions

 

 

 

 

First-Class Functions: passing functions as arguments

var years = [1990, 1965, 1937, 2005, 1998];

function arrayCalc(arr, fn){ //array와 function을 매개변수로 받아온다.
    var arrRes =[]; // 새배열생성
    for(var i = 0 ; i < arr.length; i++ ){ //배열의 길이만큼 루프
        arrRes.push(fn(arr[i])); //새배열에 펑션의 결과를 넣어줌
    }
    return arrRes; // 값을 리턴
}

function calculateAge(el){ //생년
    return 2016-el;
}

function isFullAge(el){ //나이
    return el >= 18;
}

function maxHeartRate(el){ //나이
    if(el >=18 && el<=81){
    return Math.round(206.9 - (0.67 * el));// Math.round() 소수점 계산 출력
    }else{
        return -1;
    }
}

var ages = arrayCalc(years, calculateAge); // arrayCalc에 years 배열과 calculateAge 함수를 매개변수로 넣어준다.
var fullAges = arrayCalc(ages, isFullAge);
var heartRates = arrayCalc(ages, maxHeartRate);

console.log(ages);//[26, 51, 79, 11, 18]
console.log(fullAges);//[true, true, true, false, true]
console.log(heartRates);//[189, 173, 154, -1, 195]

=> this way is much readable and mergeable than create one big function and calculate every elements. (simple technique to make a clean code)

 

 

 

 

 

 

First-Class Functions: functions renturning functions

function interviewQuestion(job){
    if(job==='designer'){
        return function(name){
            console.log(name + ', can you please explain what UX design is?');
        }
    }
    else if(job==='teacher'){
        return function(name){
            console.log(name+', what subject do you teach?');
        }      
    }
    else{
        return function(name){
            console.log('hi,'+name+'! what do you do?');
        }
    }
}

var teacherQuestion = interviewQuestion('teacher');
var designerQuestion = interviewQuestion('designer');

teacherQuestion('John');
designerQuestion('Jane');
designerQuestion('Mark');

interviewQuestion('teacher')('Mark');