在Javascript中测试嵌套对象未定义 [英] Testing nested objects as undefined in Javascript

问题描述

可能重复：

javascript测试是否存在嵌套对象密钥

我正在尝试通过测试某个对象不是 来构建 formset 的错误消息undefined ，如果它不是 undefined ，那么我最终会用该错误消息填充它。主要问题是我必须验证每个嵌套对象是否为 undefined ，这会导致一些非常难看的代码。下面是示例：

I'm attempting to construct an error message for a formset by testing if a certain object is not undefined, and if it's not undefined, then I end up populating it with that error message. The main problem is that I have to validate if each nested object is undefined, which results in some pretty ugly code. Here's the example:

errorsForField: function(fieldName, formsetName, formNumber) {
            if (typeof this.model.errors != 'undefined'){

                var fieldError = document.createElement('span');
                $(fieldError).addClass('field-error');

                // THE FOLLOWING LINE THROWS ERROR.
                if (formsetName && _.isUndefined(this.model.errors[formsetName][fieldName]) != true) {
                    $(fieldError).text(this.model.errors[formsetname][fieldName]);
                } else if (typeof this.model.errors[fieldName] != "undefined"){
                    $(fieldError).text(this.model.errors[fieldName]);
                }

                this.errors[fieldName] = fieldError.outerHTML;
                return fieldError.outerHTML; 
            }
            return false; 
        },

我收到一条错误消息，指出我无法确定 [fieldName] 未定义对象 this.model.errors [formsetName] 。换句话说，我必须首先确定 this.model.errors [formsetName] 是否为空，然后然后测试 [fieldname] 是 undefined 。

I get an error stating that I cannot determine [fieldName] of an undefined object this.model.errors[formsetName]. In other words, I have to first determine if this.model.errors[formsetName] is empty and then test if [fieldname] is undefined.

这似乎是一个非常麻烦的解决方案。有关更改此内容的任何建议吗？

This seems like a really cumbersome solution. Any suggestions for changing this?

推荐答案

您可以创建一个库函数，它将属性名称作为参数并返回最终值，如果它存在，或者为null：

You can create a library function that takes property names as parameters and returns the final value if it exists, or null:

function TryGetPropertyValue(o, propertyName1 /*, ... propertyNameN */) {
    var names = [].slice.call(arguments, 1);
    while (o && names.length) {
        o = o[names.shift()];
    }
    return names.length ? null : o;
}

称之为：

var err = TryGetPropertyValue(this.model.errors, formsetName, fieldName) ||
          TryGetPropertyValue(this.model.errors, fieldName);
if (err != null) {
    $(fieldError).text(err);
}

如果你想要它返回 undefined 而不是 null 如果找不到该字段，您可以稍微更改该函数：

If you want it to return undefined instead of null if the field is not found, you can change the function slightly:

function TryGetPropertyValue(o, propertyName1 /*, ... propertyNameN */) {
    var names = [].slice.call(arguments, 1);
    while (o && names.length) {
        o = o[names.shift()];
    }
    if (names.length == 0) {
        return o;
    }
}

http://jsfiddle.net/HbggQ/

这篇关于在Javascript中测试嵌套对象未定义的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！