proxy で undefined でもチェーンさせる

pxpchain.js

function l(val){
	var fn = () => {}
	fn.val = val
	return new Proxy(fn, {
		get: getTrap,
		apply: function(target, _this, args){
			if(args.length === 0){
				return target.val
			}
			var [apply_fn, ...apply_args] = args
			if(typeof apply_fn === "function"){
				return l(apply_fn.call(_this, target.val, ...apply_args))
			}
		}
	})
	
	function getTrap(target, name){
		if(name === "toString"){
			return method(target.val == null
				? _ => target.val
				: target.val.toString.bind(target.val)
			)
		}else if(name === "valueOf"){
			return method(target.val == null
				? _ => target.val
				: target.val.valueOf.bind(target.val)
			)
		}else if(target.val != null && (name in Object(target.val))){
			var prop = target.val[name]
			if(typeof prop === "function"){
				return method(prop.bind(target.val))
			}else{
				return l(prop)
			}
		}else{
			return l()
		}
	}
	
	function method(fnval){
		var fn = () => {}
		fn.val = fnval
		
		return new Proxy(fn, {
			get: getTrap,
			apply: function(target, _this, args){
				return l(target.val(...args))
			}
		})
	}
}

/*
l([1,2,3]).forEach(e => console.log(e))
l("abc").match(/a/)[4].a.b.c()
*/