javascript - How to create a function to check for property of an object in javascript, and set it if it's not there

Question

I have this code...

var suitcase = {
    shirt: "Hawaiian"
};

var checkProp = function(obj, prop, val){
if(obj.hasOwnProperty(prop)){
    console.log(obj.prop);
} else {
    obj.prop = val;
    console.log(obj.prop);
}
};
checkProp("suitcase","shorts","blue");

and when I run it, it returns undefined. On the surface it looks fine. No syntax problems or similar things like that. What would I have to do to get this to work?

Answer 1

suitcase is a var, not a string. Instead, it should read

checkProp(suitcase,'shorts','blue');

Answer 2

您有几个不同的选择，但我认为您的解决方案可能有效。它只是有一个小错误。在您调用您的函数时：

checkProp('suitcase', 'shorts', 'blue);

"suitcase"当它应该是一个对象时，您已将其定义为一个字符串。尝试修复它，看看它是否有效。

编辑：

您可以尝试的另一个选择是：

var checkProp = function(obj, prop, val){
    if(obj) {
        if(!obj[prop]) {
            obj[prop] = val;
        }
        if(window.console && window.console.log) {
            console.log(obj[prop]);
        }
    }
};

Answer 3

var suitcase = {
    shirt: "Hawaiian"
};

var checkProp = function(obj, prop, val){
    if(obj.hasOwnProperty(prop)){
        console.log(obj[prop]);
    } else {
        obj[prop] = val;
        console.log(obj[prop]);
    }
};
checkProp(suitcase,"shorts","blue");

Answer 4

通过它Object本身，而不是它的名字：

checkProp(suitcase,"shorts","blue");

另外，使用obj[prop]代替obj.prop.
（使用obj.prop，您访问的prop是对象的属性，字面意思，而不是您要查找的属性。）

除此之外，您的代码有效。不过，它可以像这样缩短：

var checkProp = function(obj, prop, val){
    obj[prop] = obj[prop] || val; // If obj[prop] exists, set it to itself (does nothing), otherwise, set it's content to `val`.
    console.log(obj.prop);
};

Answer 5

你想要的可能是 obj[prop] 而不是 obj.prop