Javascript 克隆/复制 Map 实例
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Clone/copy a Map instance
提问by sazr
How do I clone/copy a map in JavaScript?
如何在 JavaScript 中克隆/复制地图？
I know how to clone an array but how do I clone/copy a map?
我知道如何克隆数组，但如何克隆/复制地图？
var myArray = new Array(1, 2, 3);
var copy = myArray.slice();
// now I can change myArray[0] = 5; & it wont affect copy array
// Can I just do the same for map?
var myMap = new ?? // in javascript is it called a map?
var myMap = {"1": 1, "2", 2};
var copy = myMap.slice();
采纳答案by rob
A simple way (to do a shallow copy) is to copy each property of the source map to the target map:
一个简单的方法（做一个浅拷贝）是将源映射的每个属性复制到目标映射：
var newMap = {};
for (var i in myMap)
newMap[i] = myMap[i];
NOTE: newMap[i] could very well be a reference to the same object as myMap[i]
注意：newMap[i] 很可能是对与 myMap[i] 相同对象的引用
回答by tswaters
With the introduction of Maps in JavaScript it's quite simple considering the constructor accepts an iterable:
随着 JavaScript 中 Maps 的引入，考虑到构造函数接受一个可迭代对象，这非常简单：
var newMap = new Map(existingMap)
Documentation here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
此处的文档：https: //developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
回答by Joshua Michael Waggoner
Very simple to clone a map since what you're talking about is just an object. There is a Mapin ES6 that you should look up, but to copy an object, just use Object.assign()
克隆地图非常简单，因为您所谈论的只是一个对象。Map在 ES6 中有一个你应该查找的，但是要复制一个对象，只需使用Object.assign()
let map = {"a": 1, "b": 2}
let copy = Object.assign({}, map);
You can also use cloneDeep()from Lodash
您也可以cloneDeep()从 Lodash使用
let copy = cloneDeep(map);
回答by Pastor Bones
JQuery has a method to extend an object (merging two objects), but this method can also be used to clone an object by providing an empty object.
JQuery 有一个方法来扩展一个对象（合并两个对象），但是这个方法也可以通过提供一个空对象来克隆一个对象。
// Shallow copy
var newObject = jQuery.extend({}, oldObject);
// Deep copy
var newObject = jQuery.extend(true, {}, oldObject);
More information can be found in the jQuery documentation.
更多信息可以在jQuery 文档中找到。
回答by alex
There is nothing built in.
没有内置任何东西。
Either use a well tested recursive property copier or if performance isn't an issue, serialise to JSON and parse again to a new object.
要么使用经过良好测试的递归属性复制器，要么如果性能不是问题，则序列化为 JSON 并再次解析为新对象。
回答by Nicole
There is no built-in clone/copy. You can write your own method to either shallow or deep copy:
没有内置的克隆/复制。您可以将自己的方法编写为浅拷贝或深拷贝：
function shallowCopy(obj) {
var result = {};
for (var i in obj) {
result[i] = obj[i];
}
return result;
}
function deepCopy(obj) {
var result = {};
for (var i in obj) {
// recursion here, though you'll need some non-trivial logic
// to avoid getting into an endless loop.
}
return result;
}
All objects in Javascript are dynamic, and can be assigned new properties. A "map" as you refer to it is actually just an empty object. An Array is alsoan object, with methods such as sliceand properties like length.
Javascript 中的所有对象都是动态的，并且可以分配新的属性。您所指的“地图”实际上只是一个空对象。Array也是一个对象，具有诸如 之slice类的方法和属性length。
回答by robdc
If you need to make a deep copy of a Map you can use the following:
如果您需要制作 Map 的深层副本，您可以使用以下方法：
new Map(JSON.parse(JSON.stringify(Array.from(source))));
Where sourceis the original Map object.
source原始 Map 对象在哪里。
Note this may not be suitable for all use cases where the Map values are not serializable, for more details see: https://stackoverflow.com/a/122704/10583071
请注意，这可能不适用于 Map 值不可序列化的所有用例，有关更多详细信息，请参见：https: //stackoverflow.com/a/122704/10583071
回答by Dmitriy Pichugin
I noticed that Map should require special treatment, thus with all suggestions in this thread, code will be:
我注意到 Map 应该需要特殊处理，因此在这个线程中的所有建议中，代码将是：
function deepClone( obj ) {
if( !obj || true == obj ) //this also handles boolean as true and false
return obj;
var objType = typeof( obj );
if( "number" == objType || "string" == objType ) // add your immutables here
return obj;
var result = Array.isArray( obj ) ? [] : !obj.constructor ? {} : new obj.constructor();
if( obj instanceof Map )
for( var key of obj.keys() )
result.set( key, deepClone( obj.get( key ) ) );
for( var key in obj )
if( obj.hasOwnProperty( key ) )
result[key] = deepClone( obj[ key ] );
return result;
}
回答by Shubham Kumar
A new and elegant way of doing this:
一种新的优雅的方式来做到这一点：
var map1 = {"a": "b"};
var map2 = {...map1};
