Question

chapter6

My english is poor can’t describe the problem in detail so I paste my practice code:http://jsbin.com/exusox/3/edit

Endless loop when you click the butten.

I’ve tested my code，I found the endless loop in this code:

function extractFootnotes(paragraphs){
    var footnotes=[],currentNum=0;
    function dealWithFootnote(fragment){
      if(fragment.type=="footnote"){
        currentNum++;
        fragment.number=currentNum;
        footnotes.push(fragment);
        return {type:"reference",number:currentNum};
      }
      else{
        return fragment;
      }
    }
    //run here ,endless loop happened.I've tested forEach,the i++ can't work.
    forEach(paragraphs,function(paragraph){
      paragraph.content=map(dealWithFootnote,paragraph.content);
    });

    return footnotes;
  }


  function forEach(array,action){
    for(i=0;i<array.length;i++)
      action(array[i]);
  }

  function map(func,array){
    var result=[];
    forEach(array,function(element){
      result.push(func(element));
    });
    return result;
  }

Why this happen and How can I reduce my code?Thanks.

My Practice Code

Answer 1

The variable “i” in your “forEach” function is a global variable. You should declare it with var:

function forEach(array, action) {
  var i;
  // ... etc
}

Thus when one call to “forEach” involves an action that will itself call “forEach”, the same variable “i” will be reset.

It’s a good idea to put this at the top of your code:

"use strict";

That tells the interpreter to apply some newer rules to the code, and it’d show you an error like that.