javascript - 字符串中每个字符的出现

Question

如何编写 JavaScript 代码来计算字符串中每个字符的出现次数？

e.g 
String is : Hello World 

Output :  
count of H -> 1
count of e -> 1
count of l -> 3
count of o -> 2 
count of r -> 1
count of d -> 1 
count of W -> 1 

Answer 1

var counts = {};
yourstring.split('').map(function(ch) {
  counts[ch] = (counts[ch] || 0) + 1;
});

或者时髦地使用map/reduce:

var counts = yourstring.split('').reduce(function(dst, c) {
  dst[c] = (dst[c] || 0) + 1;
  return dst;
}, {});