如何创建函数来检查javascript中对象的属性，如果不存在则进行设置

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

Pass the Object itself, not it's name:

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

Also, use obj[prop] instead of obj.prop .
(With obj.prop , you're accessing the prop property of the object, literally, not the property you're looking for.)

Other than that, your code works. It could be shortened like this, though:

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 3

您想要的可能是obj [prop]而不是obj.prop

Answer 4

You have a few different options but I think your solution may work. It just has a small error. In your call to your function:

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

You have "suitcase" defined as a string when it should be an object. Try fixing that and see if it works.

Edit:

Another option you could try would be this:

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 5

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");