javascript - JS : How to return 'undefined' instead of throwing error 'cannot read property x of undefined'

Question

当父属性不存在时，让 js 返回 undefined 而不是抛出错误的最佳方法是什么？

示例

a = {}
b = a.x.y.z
// Error: Cannot read property 'value' of undefined
// Target result: b = undefined

Answer 1

您必须检查每个属性是否存在:

var b;
if (a.x && a.x.y && a.x.y.z) {
    b = a.x.y.z
}

或者，类似于另一张海报的“safeGet”功能:

var get = function (obj, ns) {
    var y = ns.split('.');
    for(var i = 0; i < y.length; i += 1) {
        if (obj[y[i]]) {
            obj = obj[y[i]];
        } else {
            return;
        }
    }
    return obj;
};

用途:

var b = get(a, 'x.y.z');