06-listArr.js

function typeOf(obj) {
    return Object.prototype.toString.call(obj).replace(/\[object\s|]/g, '');
}

function isArrayLike(obj) {
    const length = !!obj && 'length' in obj && obj.length; //判断是否为数组或数组对象，获取长度
    
    const type = typeOf(obj); // 获取类型
    return (
        type === 'Array' ||  
        length === 0 ||
        (typeof length === 'number' && length > 0 && length - 1 in obj)
    );
}


/**
 * 遍历对象或数组，或者类数组，例如React中的children对象、arguments等
 * @param  {Object|Array}   obj
 * @param  {Function} callback fn(n, i) or fn(val, key)
 * @param  {Number}   [direction = 1] 是否倒序遍历，只对数组有效
 * @return {Object|Array}
 *
 * @example
 * // 遍历数组
 * object.each([100, 200, 300], (n, i) => console.log(n, i));
 * // 遍历json对象
 * object.each({a: 100, b: 200}, (value, key) => console.log(key, value));
 * // 遍历React子节点
 * object.each(this.props.children, (child, index) => console.log(child));
 * // 遍历arguments
 * object.each(arguments, (arg, i) => console.log(arg));
 */
function each(obj, callback, direction=1) {
    console.log(direction)


    const reversed = true;
    const length = obj.length;
    let value,
        i = reversed ? length - 1 : 0;

    if (isArrayLike(obj)) {
        for (; i < length && i >= 0; reversed ? i-- : i++) {
            value = callback.call(obj[i], obj[i], i);

            if (value === false) {
                break;
            }
        }
    } else {
        for (i in obj) {
            /* istanbul ignore else */
            if (obj.hasOwnProperty(i)) {
                value = callback.call(obj[i], obj[i], i);

                if (value === false) {
                    break;
                }
            }
        }
    }

    return obj;
}


each([1,2,3], (value, key) => console.log(key, value) );