为什么更新一个对象的属性会改变另一个对象?

2022-01-20 00:00:00 复制 object javascript

我正在通过 ajax 将 JSON 数据加载到一个对象中，将该对象复制到新对象(initData 和 newData).当我更改 newData 的属性时，initData 的属性也会更改.为什么会这样?

I'm loading JSON data into an object via ajax, copying that object to new objects (initData and newData). When I change the property of newData, the property of initData also changes. Why is this happening? 

var initData = {};
var newData = {};    

function load_data(NDB_No){
    $.getJSON(('scripts/jsonencode.php?q=' + NDB_No), function(data) {

        for (prop in data){
            initData[prop] = data[prop];
            newData[prop] = data[prop];
        }

    console.log('init data: ' + initData.properties.Protein); // "init data: 0.259"
    console.log('new data: ' + newData.properties.Protein); // "new data: 0.259"

     var n = parseFloat(newData.properties.Protein);
     newData.properties.Protein = n+1;

    console.log('init data: ' + initData.properties.Protein + 'new data: ' + newData.properties.Protein); 
    // "init data: 1.259 new data: 1.259"
    // why are these the same when I only updated newData object?


    });


}

推荐答案

看起来 data[prop] 是一个对象(因为你后面提到 newData.properties.Protein).对象总是通过引用传递，变量只是指向它的指针.

It looks like data[prop] is an object (since you are later referring to newData.properties.Protein). Objects are always passed by reference, with the variable just being a pointer to it.

由于您首先获取的是 JSON，因此您的对象是支持 JSON 的，因此您可以使用它来克隆"对象:

Since you're getting JSON in the first place, your object is JSON-able, so you can use that to "clone" the object:

$.getJSON(...,function(data) {
    initData = JSON.parse(JSON.stringify(data));
    newData = JSON.parse(JSON.stringify(data));
});

这将确保对象是分开的.还有其他方法可以做到这一点，但是这种方法通过使用内置方法避免了手动递归(总是更快)

This will ensure that the objects are separate. There are other ways to do this, but this one avoids the manual recursion by using built-in methods (always faster)

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