带2个解析数组的For循环

Question

I have 2 arrays

var a = [
    "4",
    "@",
    "/\\",
    "/-\\",
    "^",
    "∂",
    "λ",
    "α",
    "(!",
    "Z",
    "α"
];
var r = [
    "1²",
    "2",
    "?",
    "P\\",
    "[\"/_",
    "l\"/_",
    "|-",
    "|2",
    "|?",
    "®",
    "12",
    "/2",
    "I2",
    "|^",
    "|~",
    "(r)",
    "|`",
    "l2",
    "Я",
    "ʁ",
    "я"
];

I need to pars into 1 for statement both arrays

Here is what I have:

for (var index_a=0, index_r=0; index_a < a.length, index_r < r.length ; ++index_a, ++index_r ) {
    new_a = a[index_a];
    console.log(new_a);
    new_r = r[index_r];
    console.log(new_r);
};

Output:

the element from A array: 4
the element from R array: 1²
the element from A array: @
the element from R array: 2
the element from A array: /\
the element from R array: ?
the element from A array: /-\
the element from R array: P\
the element from A array: ^
the element from R array: ["/_
the element from A array: ∂
the element from R array: l"/_
the element from A array: λ
the element from R array: |-
the element from A array: α
the element from R array: |2
the element from A array: (!
the element from R array: |?
the element from A array: Z
the element from R array: ®
the element from A array: α
the element from R array: 12
the element from A array: undefined
the element from R array: /2
the element from A array: undefined
the element from R array: I2
the element from A array: undefined
the element from R array: |^
the element from A array: undefined
the element from R array: |~
the element from A array: undefined
the element from R array: (r)
the element from A array: undefined
the element from R array: |`
the element from A array: undefined
the element from R array: l2
the element from A array: undefined
the element from R array: Я
the element from A array: undefined
the element from R array: ʁ
the element from A array: undefined
the element from R array: я

The problem is that one array is longer then the another one, and after finishing parsing the shortest one it continues to the longest one but the value for the shortest one is undefined. I need that when the shortest array ends, the last value to be saved. How can I do this. Thank you.

Answer 1

Check the value that you trying to reference from the short array. If it's undefined take the value from the last item in the short array. The ?: operator can check for this

Something like this: new_a = a[index_a]=='undefined'?a[a.length-1]:a[index_a];

Answer 2

I'm sure there can be a 1001 actually quite interesting answers on how to do this, but given your setup that you've shown above, the quickest way would simply be to surround:

if(index_a < a.length){
  new_a = a[index_a];
  console.log(new_a);
}

Now if you have 5 arrays you need to do this with, it's going to get cumbersome to have to brute force each one with a statement. A more fun way would be to start thinking in terms of another method that returns back the nth element of an array if it exists, and nothing if it doesn't. That way you can ignore the return value if it is nothing, but use it if it exists.

If all the arrays in question return back nothing, then you're done.

A little simplistic, since there will be some edge cases that can be interesting to have to consider, but this might be a nice way to get going and learn more about those edge cases, or even exception throwing and catching.

Lots of neat ways to get this done.