带有for循环的Javascript数组，只返回最后一个元素

Question

I have a for loop, that adds data into an array . but when I console.log the array, it is full of the last item of the for loop!

Here is my code :

var materialsData = results[1].data, // results[1].data is a http.get return
ln = Object.size(materialsData),
materials = [],
material = {};
material['Product'] = {};

for (var i = 0; i < ln; i++) {
    material.Product['Name'] = materialsData[i].Product.Name;
    material.Product['Id'] = materialsData[i].Product.Id;
    material.StartingDate = materialsData[i].StartingDate.replace("T00:00:00", "").split('-').reverse().join('-');
    material.Device = materialsData[i].Device;
    materials.push(material);
}

Answer 1

You are updating and pushing the same object reference again and again so the object holds the last element values. Instead, initialize the object holding variable inside the for loop beginning.

for(var i=0; i<ln; i++){
  // initialize the object
  var material = { Product : {}, Id : {}};

  material.Product['Name'] = materialsData[i].Product.Name;
  material.Product['Id'] = materialsData[i].Product.Id;
  material.StartingDate = materialsData[i].StartingDate.replace("T00:00:00", "").split('-').reverse().join('-');
  material.Device = materialsData[i].Device;
  materials.push(material);
}

---

Or directly define the object as the argument of push method without holding it to any variable.

for (var i = 0; i < ln; i++) {
  materials.push({
    Product: {
      Name: materialsData[i].Product.Name,
      Id: materialsData[i].Product.Id,
    },
    StartingDate: materialsData[i].StartingDate.replace("T00:00:00", "").split('-').reverse().join('-'),
    Device: materialsData[i].Device
  })
}

Answer 2

Define material in the for block. As Objects are passed by reference same object is updated and pushed to the array.

for (var i = 0; i < ln; i++) {
    var material = {
        Product : {
            Name : materialsData[i].Product.Name,
            Id : materialsData[i].Product.Id,
        },
        StartingDate : materialsData[i].StartingDate.replace("T00:00:00", "").split('-').reverse().join('-'),
        Device : materialsData[i].Device
    };
    materials.push(material);
}

Additionally, You can use Array.map()

var materials = materialsData.map(function(m){
    return {
        Product : {
            Name : m.Product.Name,
            Id : m.Product.Id,
        },
        StartingDate : m.StartingDate.replace("T00:00:00", "").split('-').reverse().join('-'),
        Device : m.Device
    };
})

Answer 3

You are indeed referencing the same object. For me the trick was to wrap the object in question around JSON.stringify() and then within the loop I call JSON.parse() on the resulting string to turn it back

 var materialsDataString = JSON.stringify(results[1].data), // results[1].data is a http.get return ln = Object.size(materialsData), materials = [], material = {}; material['Product'] = {}; for (var i = 0; i < ln; i++) { var materialsData = JSON.parse(materialsDataString) material.Product['Name'] = materialsData[i].Product.Name; material.Product['Id'] = materialsData[i].Product.Id; material.StartingDate = materialsData[i].StartingDate.replace("T00:00:00", "").split('-').reverse().join('-'); material.Device = materialsData[i].Device; materials.push(material); }

.