SOURCE

let a = [
"1","2","3","4"
];

let aEntries = a.entries();
console.log(aEntries);
console.log(JSON.stringify(aEntries));
console.log(aEntries.next().value);//[0,'1']位置0的值为1
console.log(aEntries.next().value);
console.log(aEntries.next().value);
console.log("====");
let index3 = aEntries.next();

console.log(JSON.stringify(index3));
console.log("位置为"+index3.value[0]);
console.log("值为"+index3.value[1]);
let index4 = aEntries.next();
console.log(JSON.stringify(index3));
console.log(JSON.stringify(index4));//
let index5 = aEntries.next();
let str="";
for(let key in index5){
str+=(key+" ")
}
console.log(str)
console.log(str.value===undefined)