myReduce实现

Array.prototype.myReduce = function(reducer, initialValue) {
    const hasInitial = arguments.length > 1;
    let ret = hasInitial ? initialValue : this[0];
    for (let i = hasInitial ? 0 : 1; i < this.length; i++) {
        ret = reducer.call(undefined, ret, this[i], i, this);
    }
    return ret;
}

// 或者极简版本
Array.prototype.myReduce = function(reducer, initialValue) {
    let ret = initialValue;
    for (let i = 0; i < this.length; i++) {
        ret = reducer(ret, this[i], i, this);
    }
    return ret;
}

some filter https://chaiguanpeng.github.io/2018/05/29/js%E6%95%B0%E7%BB%84%E4%B8%ADfilter%E3%80%81map%E3%80%81reduce%E3%80%81find%E7%AD%89%E6%96%B9%E6%B3%95%E5%AE%9E%E7%8E%B0%E7%9A%84%E5%8E%9F%E7%90%86/