[javascript] 배열 키값 가져오기

var arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']
 
 
// array like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.keys(obj)); // console: ['0', '1', '2']
 
 
// array like object with random key ordering
var anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.keys(anObj)); // ['2', '7', '100']
 
 
// getFoo is property which isn't enumerable
var myObj = Object.create({}, {
  getFoo: {
    value: function () { return this.foo; }
  } 
});
myObj.foo = 1;
console.log(Object.keys(myObj)); // console: ['foo']
 
 
var anObj = { 100: 'a', 2: 'b', 7: 'c' };
var arr = {};
Object.keys(anObj).forEach(d => {    
    arr[anObj[d]] = d;
});
console.log(arr); // console: {b: "2", c: "7", a: "100"}