[英]ES6 map is throwing error on array of object
const normalizeEventTypes = nextProps.events.space_events.map(obj, i =>
obj.id
)
I code obj is not defined, my array of object look like this 我没有定义代码obj,我的对象数组看起来像这样
{
"space_events": [{
"id": 1,
"name": "Anniversaries"
},
{
"id": 2,
"name": "Brand Rollout"
}
}]
}
am I missing something? 我错过了什么吗?
You forgot to use ()
, write it like this: 你忘了使用
()
,像这样写:
const normalizeEventTypes = nextProps.events.space_events.map((obj, i) =>
obj.id
)
Reason : 原因 :
You are using obj and index both parameters in map
callback function so you need to use ()
to wrap the parameters, like this: 您在
map
回调函数中使用obj和索引两个参数,因此您需要使用()
来包装参数,如下所示:
a = b.map((i,j) => i)
These ()
are optional when we want to use only one parameter, like this: 当我们只想使用一个参数时,这些
()
是可选的,如下所示:
a = b.map(i => i)
Different ways of using map
: 使用
map
不同方式:
1. a.map(i => i + 1); //when index is not required
1.
a.map(i => i + 1); //when index is not required
a.map(i => i + 1); //when index is not required
2. 2。
a.map(i => { //when want to do some calculation
//some calculation
return //something;
})
3. a.map((i,j) => i + j) //when want to use the index of item
3.
a.map((i,j) => i + j) //when want to use the index of item
Check the working snippet: 检查工作代码段:
let data = { "space_events": [{ "id": 1, "name": "Anniversaries" }, { "id": 2, "name": "Brand Rollout" } ] } let result = data.space_events.map((obj,i) => obj.name); console.log('result', result);
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