ES6，数组遍历

const arr1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k']
for (let index of arr1.keys()) {
  console.log(index);
}

0  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10 

for (let val of  arr1.values()) {
  console.log(val);
}

a 
b 
c 
d 
e 
f 
g 
h 
i 
j 
k 

for (let [index, val] of arr1.entries()) {
  console.log(index, val);
}

0 'a'
1 'b'
2 'c'
3 'd'
4 'e'
5 'f'
6 'g'
7 'h'
8 'i'
9 'j'
10 'k'

let arrEntries=arr1.entries();
let entry=arrEntries.next();
while(!entry.done){
  console.log(entry.value);
  entry=arrEntries.next();
}

[ 0, 'a' ]
[ 1, 'b' ]
[ 2, 'c' ]
[ 3, 'd' ]
[ 4, 'e' ]
[ 5, 'f' ]
[ 6, 'g' ]
[ 7, 'h' ]
[ 8, 'i' ]
[ 9, 'j' ]
[ 10, 'k' ]