用map reduce filter spilt join实现

 B

const counter = (function () {
	let arr = [];
	return function () {
		arr.push(1);
		return arr.reduce((pv, v)=>pv+v);
	};
})();
console.log(counter())
console.log(counter())
console.log(counter())

 A

((arr)=>{
	let sum = arr.reduce((pv, v)=>pv+v);
	console.log(sum);
})([1,2,3,.5,100]);

        // 只用map reduce filter spilt join 方法实现下面功能
        const counter = () => {
            const str = window.str || ''
            window.str = str + ','
            return str.split(',').length
        }
        console.log(counter())
        console.log(counter())
        console.log(counter())
        console.log(counter())
        console.log(counter())

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