Question

我想尽可能多地了解这是如何工作的 - 特别是因为它涉及三元的使用和包含两个点差的对象参数。

rows = rows.map(row => (changed[row.ID] ? { ...row, ...changed[row.ID] } : row));

首先 - 传递给地图的对象的结构如下： changed形如此{"75864":{"ActType":"DEADLINE"}}

rows的格式如下（例如）：

[{
    "ID": 75864,
    "NextDate": "2018-03-02T00:00:00",
    "NextTime": "1030am",
    "MatterID": 14116,
    "Descr": " Responses to pending discovery",
    "StatusID": 19,
    "Actor_s_": null,
    "Accrued": 0,
    "Go": "",
    "AspNetUserID": null,
    "DomainID": 2,
    "UserID": 1,
    "StatusType": "Pending",
    "ActTypeID": 50,
    "ActType": "DEADLINE",
    "MatterName": "WYNBAS                   "

Answer 1

这是＆＃34;合并＆＃34; row和changed[row.ID]成为一个对象。让我们来看看当row是具有ID＆＃34; 75864＆＃34;

的

// row: {"ID": 75864, "ActType": "DEADLINE", (more properties)}
// changed: {"75864": {"ActType": "OTHER ACTION"}}
// (Note - I changed `changed` so that the ActType specified is different from
//  what's already in the row object, otherwise it's really difficult for me to
//  demonstrate exactly what's happening here.)

// This is the body of the arrow function:
return changed[row.ID] ? { ...row, ...changed[row.ID] } : row

// Well, changed[row.ID] does exist:
// changed[row.ID]: {"ActType": "OTHER ACTION"}

// So we take this branch of the ternary:
return { ...row, ...changed[row.ID] }

// Basically, this expression works like an array spread, but for objects.
// As a refresher, here's what an array spread might look like:
//
// a = [1, 2, 3]
// b = ['cat', 'dog', 'armadillo']
// c = [...a, ...b]
// c: [1, 2, 3, 'cat', 'dog', 'armadillo']
//
// The array spread works by creating a completely new, empty array. Then
// it adds the items of each array that's spread into it; so first it adds
// all the items of a (1, 2, 3), then all the items of b (cat, dog, armadillo).

// Object spread works pretty much the same way. First we create a completely
// new object: {}.
// Then we add all the properties of row: {ID: 75864, ActType: "DEADLINE",
// "MatterID": 14116, (more properties)}.
// Then it adds the the properties of changed[row.ID]. This is the important
// part, because changed[row.ID] actually *overwrites* any properties that
// we've already added from "row". This makes the result look like this:
return {ID: 75864, ActType: "OTHER ACTION", MatterID: 14116, (more properties)}

// Note that the return value's ActType property is OTHER ACTION, not DEADLINE!

时会发生什么。

row

请注意，对象传播与使用空对象作为第一个参数的Object.assign基本相同。（Object.assign从第二个，第三个等参数中获取所有属性，并在第一个参数上设置它们。这意味着它实际上会更改 - 变异 - 它的第一个参数;而在这里，我们不会变异{{1} }，我们基于 row（和changed[row.ID]）返回一个全新的对象。）因此，使用Object.assign编写代码将如下所示：< / p>

return Object.assign({}, row, changed[row.ID])

Answer 2

如果row.ID值与changed对象中具有“truthy”值的键匹配，

然后您返回一个新对象，其中包含row的所有值（您展开row），并向此新对象添加匹配的changed对象的值（你传播了changed）的真实价值。

您只需返回给定的行。

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JavaScript ES6 - 这是扩展语法还是其他语法？

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