映射返回对象

我得到了这个数组,

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launches:4 },
{ country:'Japan', launches:3 }
];

我需要做什么才能返回一个数组映射，每个数组增加10

发射

价值，这是我的第一个方法,

const launchOptimistic = rockets.map(function(elem){
return (elem.country, elem.launches+10);
});
console.log(launchOptimistic);
269709 次浏览
小开

You're very close already, you just need to return the new object that you want. In this case, the same one except with the launches value incremented by 10:

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launches:4 },
{ country:'Japan', launches:3 }
];


const launchOptimistic = rockets.map(function(elem) {
return {
country: elem.country,
launches: elem.launches+10,
}
});


console.log(launchOptimistic);

小开

map rockets and add 10 to its launches:

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launches:4 },
{ country:'Japan', launches:3 }
];
rockets.map((itm) => {
itm.launches += 10
return itm
})
console.log(rockets)

If you don't want to modify rockets you can do:

var plusTen = []
rockets.forEach((itm) => {
plusTen.push({'country': itm.country, 'launches': itm.launches + 10})
})
小开

If you want to alter the original objects, then a simple Array#forEach will do:

rockets.forEach(function(rocket) {
rocket.launches += 10;
});

If you want to keep the original objects unaltered, then use Array#map and copy the objects using Object#assign:

const newRockets = rockets.map(function(rocket) {
const newRocket = Object.assign({}, rocket);
newRocket.launches += 10;
return newRocket;
});
小开
最佳答案

Use .map without return in simple way. Also start using let and const instead of var because let and const is more recommended 

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launches:4 },
{ country:'Japan', launches:3 }
];


const launchOptimistic = rockets.map(elem => (
{
country: elem.country,
launches: elem.launches+10
}
));


console.log(launchOptimistic);

小开

The cleanest solution is destructuring.

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launche`enter code here`s:4 },
{ country:'Japan', launches:3 }
];
const updated = rockets.map(rocket=>{
return {...rocket,launches:rocket.launches+10}
});
小开

Considering objects can have many properties, It would be better to spread the object's content and to reassign specific properties, to achieve code that is more succinct.

const rockets = [
{ country:'Russia', launches:32 },
{ country:'US', launches:23 },
{ country:'China', launches:16 },
{ country:'Europe(ESA)', launches:7 },
{ country:'India', launches:4 },
{ country:'Japan', launches:3 }
];


const launchOptimistic = rockets.map(function(elem) {
return {
...elem,
launches: elem.launches+10,
}
});


console.log(launchOptimistic);

小开

Solution (One Liner) With a Fresh Example

Suppose the clients in your bank (including you, of course) got a bonus.

let finance = [
{funds:10050, client_id: 1020},
{funds:25000, client_id: 77},
{funds:90000, client_id: 442}
];


finance = finance.map(({funds, client_id}) => {funds = funds + 2000; return {funds, client_id}});

↑ Test & copy as is to Chrome / Firefox / Edge DevTools console ↑

This technique called Destructuring Assignment

The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from objects, into distinct variables.


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