var string = 'aa,bb,c';

​

var separator = ',';

​

​

function split(string,separator) {

  var cache = [];

  var cachInt = 0;

  var lastWord = '';

  for (var i = 0; i < string.length; i++) {

    if(string[i] === separator) {

        cachInt++

        lastWord = ''

    }

    else {

      lastWord = lastWord + string[i];

      cache[cachInt] == lastWord;

    }

  }

  return cache;

}

​

​

function splitString() {

  console.log(split('string, separator',','));

}

​