Here is original question: Getting JavaScript object key list
But if the situation is little bit more complex like:
var obj = [
{ key1: 'value1' },
{ key2: 'value2' },
{ key3: 'value3' },
{ key4: 'value4' }
]
Then how you get keys like that?
[key1,key2,key3,key4]
You can use mix of Object.keys and Array#flatMap.
let obj = [
{ key1: 'value1' },
{ key2: 'value2' },
{ key3: 'value3' },
{ key4: 'value4' },
];
let keys = obj.flatMap(Object.keys);
console.log(keys);
[].concat(...obj.map(Object.keys));.you can get keys for each object in obj and then use concat() to add it to your result array.
var obj = [
{
key1: 'value1'
},
{
key2: 'value2'
},
{
key3: 'value3'
},
{
key4: 'value4'
}
]
var keyList = [];
obj.forEach(function(o){
keyList = keyList.concat(Object.keys(o));
});
console.log(keyList);You can achieve it using Array#reduce method.
var obj = [{
key1: 'value1'
}, {
key2: 'value2'
}, {
key3: 'value3'
}, {
key4: 'value4'
}];
var res = obj
// iterate over the array
.reduce(function(arr, o) {
// get keys and push into the array
[].push.apply(arr, Object.keys(o));
// return the araray reference
return arr;
// set initial value as an empty array
}, []);
console.log(res);
// ES6 alternative
var res1 = obj.reduce((arr, o) => (arr.push(...Object.keys(o)), arr), []);
console.log(res1);
"Uncaught SyntaxError: Unexpected token {",
arr.push mutating the array inside a reduce. Why not return [...arr, Object.keys(o)], or do the same with concat?
map() method is better than reduce() ,.... That may be better I'm not sure about it :)for loop.Try with Array#reduce() and Object.keys() .Reduce create the array with in function and forEach iterate the inner Object keys
var obj = [ { key1: 'value1' }, { key2: 'value2' }, {
key3: 'value3' }, {
key4: 'value4' } ]
console.log(obj.reduce(function(a,b){
Object.keys(b).forEach(function(val){
a.push(val)
})
return a;
},[]))
array question .why?You can iterate over object properties with for in, something like this.
var obj = [
{ key1: 'value1' },
{ key2: 'value2' },
{ key3: 'value3' },
{ key4: 'value4' }
],
keysArray = [];
obj.forEach((item)=>{
for(key in item){
keysArray.push(key);
}
});
console.log(keysArray);Using Arrows, looks bit odd because of [0] :/
var obj = [
{ key1: 'value1' },
{ key2: 'value2' },
{ key3: 'value3' },
{ key4: 'value4' }
];
var result = obj.map(x => Object.keys(x)[0]);
console.log(result);And if there are more than one key value pair, then
obj.map(Object.keys).reduce((a, b) => a.concat(b));
Other ways:
[].concat(...obj.map(Object.keys));
[].concat.apply(this, obj.map(Object.keys));
Or using Lodash (which I use a lot)
_.flatten(obj.map(Object.keys))
objis not a plain object, but rather an array.