JS function currying

Function currying

Appreciated: refers to a function that accepts a plurality of parameter becomes a parameter returns function accepts a fixed form, it is easy to call again, for example, f (1) (2)

Common functions such as add

function add(a,b){
    return a+b
}
// 变为
function curry(fn){
    var firstArgs=Array.prototype.slice.call(arguments,1)  //这里，arguments的第一个参数是fn,所以从1开始
    var _cur=function(){
        var nextArgs=[...arguments]
        var allArgs=firstArgs.concat(nextArgs)
        return fn.apply(this,allArgs)
    }
    
    return _cur
}
var add1=curry(add,10)
add1(10) //20
add1(20) //30

Curry current currying a receiving function, a function for processing and return the remaining parameters so that the two successive calls, i.e. curr (add, 10) (20) returns 30

Upgrade of difficulty

At this point a simple curried complete, but if you encounter f (1) (2) (3) ... and so many times when successive calls will seem weak, at this time requires a more complex currying recursive currying

function add(){
    return [].reduce.call(arguments,(a,b)=>{
        return a+b
    },0)
}
function curry(fn){
    var len=fn.length // fn.length 指的是函数需要接受的参数长度
    var args=Array.prototype.slice.call(arguments,1) 

    var _adder= function(){
        var _args=Array.prototype.slice.call(arguments)   // 等价于arguments.slice()
        if(_args.length==0){
            return fn.apply(this,args)
        }else{
            [].push.call(args,..._args)   
            return _adder
        }
    }
    _adder.toString=function(){
        return _adder()
    }
    return _adder
}
var add1=curry(add)
console.log(add1(2)(2).toString()) //4

The difference between call and apply: Note

• Both are changing this function pointer, if the first parameter is null or undefined points to the default window
• Different call is received by the second parameter is all the arguments, and apply received is an array
• E.g. fn.call (obj, 1,2,3) fn.apply (obj, [1,2,3])

Exercise

Achieve a function, so that it can implement the following functions

add(1) //1
add(1)(2) //3
add(1)(1,2,3) //7

function add(){
    var args=[...arguments]
    
    var _adder= function(){
        var _args=Array.prototype.slice.call(arguments)
        if(_args.length==0){
            return args.reduce((a,b)=>{
                return a+b
            },0)
        }else{
            [].push.call(args,..._args)
            return _adder
        }
    }
    _adder.toString=function(){
        return _adder()
    }
    return _adder
}