javascript - Word Frequency Count, fix a bug with standard property

Question

I'm trying to build a javascript function which would count the number of occurrences of each word in an input array.

Example :

Input

a=["a","booster","booster","constructor","adam","adam","adam","adam"]

Output:

"a":1
"booster":2
"constructor":1
"adam":4

Output should be dict-alike.

I'm new to javascript and I tried to use a dict. But objects have a property called "constructor", so cnt["constructor"] seems not to work.

Here is my code and the result:

var cnt={};
console.log("constructor");

for(var i=0;i<a.length;++i)
{
    if(! (a[i] in cnt))
        cnt[a[i]]=0;
    else
        cnt[a[i]]+=1;
}

for(var item in cnt)
    console.log(item+":"+cnt[item]);

Result:

You can see that 1 is added to constructor of cnt as a string.

Answer 1

function count(arr){
  return arr.reduce(function(m,e){
    m[e] = (+m[e]||0)+1; return m
  },{});
}

The idea behind are

• the use of reduce for elegance
• the conversion of m[e] to a number using +m[e] to avoid the constructor (or toString) problem

Demonstration