array + charAt issue

Question

The following code output a k[i].charAt is not a function error. The strange thing is that there is no error - and the result is correct - if instead of i I put a number k[1].charAt(0). Same thing with indexOf.

for (i = 0; n < arguments.length; i++) {
    k[i] = arguments[i];
    if (k[i].charAt(0) == "["){
        k[i] = eval(k[i]);
    }
}

what is `k`? your code doesnt include your definition of `k`. — xGeo, May 11 '17 at 06:11
What is `n`? Have you tried debugging this yourself, with `console.log` for example? — Sebastian Simon, May 11 '17 at 06:11
You don't seem to be updating n in your loop, so depending on what it is initially, this could go in an infinite loop. Also, your definitions of `k` and `n` are not given here. — Stuti Rastogi, May 11 '17 at 06:14
N is a typing error, even changing with i the result does not change. k is a global array defined at the beginning with var k = [] — Simone Pappalardo, May 11 '17 at 06:29
Then you should of explained that in the question to make it less ambiguous and get better responses — Mi-Creativity, May 11 '17 at 06:35

score 0 · Answer 1 · edited May 23 '17 at 11:47

This code is kind of ambiguous.

arguments represents all arguments given to a function as array-like object.
charAt is a function defined on String.prototype

So if (x.chatAt(0) == '[') { … } will only work if x is a String, otherwise you will get the Error as described above.

All in all (in es6):

const foo = (...args) => {
  for (let arg of args) {
    if (arg.chatAt(0) == '[') { … }
  }
} 

foo({}) // Error
foo('[', {}) // Error, because arg2 is not a string
foo('[', ']') // No Errors, because each arg is a String

So there are two things you could do:

convert each arg to a string, before running the test: if (''+ arg.charAt(…)) …, or if (arg.toString().charAt())
throw an Error if an Argument is not a string. To test if a variable is a String can be found here

score 0 · Answer 2 · answered May 11 '17 at 06:48

Assuming, you hand over arguments, which are JSON strings, then I suggest to use a mapping with a check and JSON.parse and avoid to use eval.

function convert() {
    return Array.prototype.map.call(arguments, function (a) {
        return a[0] === '[' ? JSON.parse(a) : a;
    });
}

console.log(convert('a', 1, '[1,2,3]'));

.as-console-wrapper { max-height: 100% !important; top: 0; }

array + charAt issue

2 Answers2