将键值（对象）对添加到数组中的所有对象

Question

My question is related to Add key value pair to all objects in array

However, the solutions don't work when I try to assign an object instead of a string, int etc.

I tried to create the new key inside map function, but it only works with non-object variables.

This works

arrObjects.map(item => item.newKey = 'xxx')

This doesn't

var obj = { a: 'a', b: 'b', c: 'c' }
arrObjects.map(item => item.newKey = obj)

Output:

 var arrOfObj = [{ name: 'eve' }, { name: 'john' }, { name: 'jane' }]; var obj = { a: 'a', b: 'b', c: 'c' } arrOfObj.map(item => item.newKey = obj); console.log(arrOfObj); 

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Answer 1

You need to use ... (spread operator)

 var arrOfObj = [{ name: 'eve' }, { name: 'john' }, { name: 'jane' }]; var obj = { a: 'a', b: 'b', c: 'c' }; arrOfObj.forEach(item => item.newKey = {...obj}); console.log(arrOfObj); 

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Alternatively, use JSON :

 var arrOfObj = [{ name: 'eve' }, { name: 'john' }, { name: 'jane' }]; var obj = { a: 'a', b: 'b', c: 'c' }; arrOfObj.forEach(item => item.newKey = JSON.parse(JSON.stringify(obj))); console.log(arrOfObj); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 2

You need to create a copy of object. By default object is assigned as reference. here ... is used to create a shallow copy

 var arrOfObj = [{name: 'eve'}, {name: 'john'}, { name: 'jane'}]; var obj = { a: 'a', b: 'b', c: 'c'} arrOfObj.forEach(item => (item.newKey = {...obj})); console.log(arrOfObj); 

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You can see some of use case here

Answer 3

One alternative is to use Object.assign() . Remenber that objects are copied by the value of the reference, that was your problem, instead of a new object for every newKey , you had multiple references to the same object.

 var arrOfObj = [ {name: 'eve'}, {name: 'john'}, {name: 'jane'} ]; var obj = { a: 'a', b: 'b', c: 'c' }; arrOfObj.map(item => item.newKey = Object.assign({}, obj)); console.log(arrOfObj); // After some modification. arrOfObj[0].newKey.a = "XXX" console.log(arrOfObj); 

Answer 4

You have to clone the item, you are adding the same object to multiple property.

See below how it should be.

 var arrOfObj = [{ name: 'eve' }, { name: 'john' }, { name: 'jane' }]; var obj = { a: "a", b: "b", c: "c" } arrOfObj.map(item => // clone the item item.newKey = JSON.parse(JSON.stringify(obj)) ); console.log(arrOfObj);