题解 | js手写filter

// 补全代码
            Array.prototype._filter = function(cb, context) {
                var arr = this || []
                var res = []
                for(let i = 0; i < arr.length; i++) {
                    var isFilter = cb(arr[i], i, this, context)
                    if (isFilter) {
                        res.push(arr[i])
                    }
                }
                return res
            }