var obj={'0':'a','1':'b','2':c'};

1.Objects.keys()
Objects.keys(obj).forEach(function(key){
console.log(key,obj[key])
})

2.for in
for(var i in obj){
console.log(i,":",obj[i])
}

3.Object.getOwnPropertyNames()
Object.getOwnPropertyNames(obj).forEach(function(key){
console.log(key,obj[key])
})

4.Reflect.ownKeys()
Reflect.ownKeys(obj).forEach(function(key){
console.log(key,obj[key])
})